There are quite a few options for players wanting a sneaky character that also has some magic potential. 
Bard classes, 
Arcane Trickster, and even 
Rangers (or a mix of these by multi-classing) could all fill this role. However, there is one combination that really stands out because of its synergy, and that is the 
Rogue Assassin / 
Pact of the Blade Warlock.
Due to this Warlock class’s unique weapon scaling and features, it is able to become more powerful when leveraging the Assassin’s brutal first round buffs and advantages. We’ll get into all the details, but if you’re interested in a unique build for 
Wyll, or a stealthy character build that starts their battles with debuffs, critical hits, and spells, then you’re in the right place.
Summary
The gist of this build is to start with a character that is a warlock (so putting a lot of points into Charisma) with the subclass 
The Great Old One. After leveling it up to five to get the double attack, multi-class to Rogue and take the Assassin route up to level 12.
When you start a fight with this character, you will want to surprise your enemies. Assassin’s always do critical hits to surprised enemies with their feature 
Assassinate: Ambush, and Warlocks have a chance to frighten enemies (and close-by enemies) with the class feature 
Mortal Reminder. After the first round, the player will have frightened the surrounding enemies and can easily manage the battlefield from there.
The main issue with this build is that you can usually talk your way out of anything because of your massive charisma stat, but if negotiations fail, then you can’t surprise your enemies. For this reason, it’s imperative to choose your battles carefully, and either go for a surprise attack or a negotiation (where you are sure to succeed).
Character Creation
There are a lot of good options for the race of this build, but we went with 
Half-Orc. The main reason being that after we have multi-classed to Assassin, we will be relying on those lovely critical hits while enemies are surprised. Orcs come with the feature, 
Savage Attacks, which adds additional damage to critical hits.
Background is also flexible, we would recommend one of the stealthier ones like Urchin or Criminal, since you will be sneaking into most fights to surprise enemies. If you’re not familiar with the 
Warlock class, then you might be confused why we’re dumping so many points into Charisma. The main reason is that it is their primary casting stat, and it will actually replace Strength and Dexterity as our weapon’s damage stat with Pact of the Blade.
Also, because we are mainly using a melee weapon and performing high-risk high-reward attacks, we want a good chunk of points in 
Constitution for survivability. As for the skill proficiencies, we found that more skills revolving around controlling conversations were the most useful.
Leveling Up
You will want to follow these level choices closely, except for the early level spell options, which will be swapped out later. Although, there is one major option for deviation with this build: you can either multi-class from Warlock to 
Rogue at level 5 or 6. If you stay in Warlock one extra level (till six), then you gain 
Entropic Ward and another spell (not a slot) up to the third level. This is an okay option if you plan on dipping more into magic, and Entropic Ward actually comes in handy when sneak attacking an enemy that missed an attack on you the round prior.
That being said, we still think that it is better for the build to get that 6th level in as a Rogue. Not only will your sneak attacks do more damage, but you will gain Evasion, helping to survive against spell damage.
Gain 1 Warlock Spellslot
- Warlock spell slots are unique; they aren’t leveled like other casters. Instead, they are always cast at the highest level the Warlock knows. To offset this, they have fewer slots, but slots are regained after short rests.
Choose Two Spells
None of these spells are mandatory to the build, and we will switch them out later, so go with what you prefer, but we chose:
Hellish Rebuke – A good reaction spell to take out weakened enemies.
Hex – Good for taking on bosses and tough opponents after you’ve exhausted your critical hits from the first couple rounds.
Choose Two Cantrips
Eldritch Blast – Since we won’t have high Dex for using ranged weapons effectively, we will be using this powerful cantrip to attack from afar.
Friends – Makes your already charismatic character even more likeable in conversations.
Choose a Subclass
Gain 1 Warlock Spellslot
Choose Two Eldritch Invocations
Both of these will further increase the effectiveness of Eldritch Blast:
- Agonizing Blast – A great cantrip that our character will use for ranged combat.
-And-
- Repelling Blast – If you’re like us and like looking for opportunities to blast enemies into chasms, then this is a no-brainer.
-Or-
- One with Shadows – If you want a stealthier approach, then this is a good choice. Go invisible in an obscured area, but you can’t move while invisible. Excellent for getting past patrolling guards when you don’t have cover to hide behind. Recharges on long rest.
Choose a Spell
Dissonant Whispers – You might be interested in grabbing 
Expeditious Retreat to more easily traverse the battlefield (and you can), but remember that you will gain Cunning Action: Dash as a Rogue, making it irrelevant. Instead, we like Dissonant Whispers to frighten enemies, and deal some damage, but again we will switch it out later.
Subclass
This is where you finally choose a Warlock Pact Boon:
- Pact of the Blade – With this pact, you can summon a weapon (and be proficient with it) or bind a held weapon. With either, the weapon will use the character’s Charisma stat instead of Strength or Dexterity. Just remember that you need to bind a held weapon, or summon a weapon, every time after you long rest.
Warlock Spells Upgraded
Your spells will now be cast at the second level, making them stronger.
Choose a New Spell
Now you have access to level 2 spells. We recommend grabbing stealthier ones to compliment the build, as you won’t be casting a lot in combat.
Invisibility – Another tool in your arsenal to get where you’re not supposed to, whether it’s to line up the perfect ambush, or snatch some valuable items.
Switch out Spell
You can only switch out one spell, but it is worth it to upgrade a spell to a higher level one.
Misty Step – It can’t be understated how useful this spell is for sneaking and navigating a battlefield. Swap it for Hellish Rebuke.
Expanded Spell List from The Great old One
Choose a Feat
Since we will be relying so heavily on our weapon, we want to buff it as much as possible.
Ability Improvement – Crank up that Charisma to 19. Note: it usually isn’t wise to leave an attribute stat on an odd number because you are missing out on a modifier improvement. So, we recommend getting that last point in charisma (making it maxed at 20) from Auntie Ethel’s Deal when fighting The Hag in Act 1.
Choose a Cantrip
- Friends – Choose if you want to have an advantage in more dialogues.
-Or-
Minor Illusion – Choose if you want a tool to distract enemies and let you sneak past them.
Choose a Spell
Mirror Image – An excellent spell for when you’re in over your head, and you need a higher Armor Class to survive a group of enemies.
Swap out a Spell
Darkness – There are plenty of opportunities to cast this on groups of archers, so they must move to attack. It also dampens the amount of eyes keeping you from sneaking during combat. Swap it out for Hex.
As with most Level 5’s, the Warlock gets a large power spike here.
Proficiency Bonus
Choose an Eldritch Invocation
Devil’s Sight – This invocation works well with the spell we acquired last level, Darkness. With the Invocation, our Warlock can see through the darkness and attack enemies inside.
Deepen Pact
Cantrip Improvement
- Eldritch Blast can now fire two bursts (at one or two enemies), and yes, they both have Repelling Blast.
Warlock Spells Upgraded
- Your spell slots are now all level 3, and you can learn level 3 spells.
Choose a Spell
Fear – Can be used on the third or fourth rounds after the fear from your critical hits have worn off. Fits the build’s name.
Swap out Spell
Expanded Spell List from The Great Old One
Multiclassing to Rogue
Sneak Attack (Melee and Ranged)
This class action comes with the rogue class. It can be used when the character has an advantage over the enemy, like when attacking from stealth, when the enemy is surprised, or when a companion is next to the enemy. Mastering this skill is essential to the build.
Pick 2 Skills (Expertise)
- Stealth – Double down on stealth to pass more checks.
-And-
- Deception – We would lean into this to make it basically always pass in conversation, but you can choose another, it’s not super important for the build.
Cunning Actions
At first, these might be confusing because you already have access to ‘Hide’, ‘Disengage’, and ‘Dash’ as regular actions. The difference is that these are used as Bonus Actions. Hide will be used the most often, and typically at the start of a turn, so the rogue can gain advantage and attack with a sneak attack.
However, after the first round, you will find that Cunning Action: Dash is very useful for crossing a distance to an enemy or to reach a vantage point.
Subclass
This is where you finally choose to be an Assassin and gain the class’s three deadly passives:
Assasinate: Initiative – You gain an advantage for attack rolls on enemies that haven’t taken their turn yet. After we get the feat ‘Alert’ next level, this passive will be much more potent.- Assasinate: Ambush – This passive turns all successful attack rolls against surprised targets into critical hits. With this build, you will want to be starting the fight sequences to gain the surprised advantage. In turn, because of Mortal Reminder, these critical hits can frighten nearby enemies.
Assassin’s Alacrity – Let’s say you sneak attack an enemy, thus starting combat. That original sneak attack action is replenished instantly, meaning you can attack again immediately if you have high initiative.
Sneak Attack Damage
Goes up from using 1D6 to using 2D6.
Proficiency Bonus
Feat
There are quite a few options, but the Alert feat is the best. It raises the character’s initiative by 5, which makes it almost always go first in the turn order. Due to the advantages of Assassinate: Initiative, this is an easy choice.
Features
Uncanny Dodge – You now only take half the damage from one normal attack once a round. This will help a lot if you fail a check or are caught behind enemy lines.
Sneak Attack Improvement
- Sneak Attack now does 3d6 damage.
Add Expertise to Two Skills
Stealth – It might be a little overkill, but stealth is really what makes this build tick, so lean into it.
Perception – Give your perception a boost, so you can find secrets and traps easier. Again, not super important, so go with something else if you really want to.
Features
- Evasion – This passive allows your character to take no damage from spells when they roll a successful dexterity saving throw (even from spells that normally do half damage on a saving throw).
Sneak Attack Improvement
- Sneak attack now does 4d6 damage.
Equipment
Act 1
- Gloves of Dexterity
- Excellent for this build because they raise the wearer’s Dexterity to 18 and increases their attack by +1. This translates to a better Armor Class, and better chances for checks, such as avoiding spell damage with Evasion. If you really want to min / max your character. You can respec and take out all the Dexterity points to put them into other attributes like Constitution.
- Can be purchased from A’jak’nir Jeera in Creche Y’llek, accessed through the mountain pass in late Act 1.
- Diadem of Arcane Synergy
- Extremely potent for this build because as you are causing frighten to enemies on the first round (through critical hits), you are buffing your weapon damage.
- Can be looted off of Ardent Jhe’rezath, in Creche Y’llek.
- Shortsword of First Blood
- If it isn’t there, it will be on a dead Duergar that’s also east of the Underdark fast travel point and up a cliff. (X: 30 Y: -161)
- This shortsword adds 1d8 piercing damage to target’s with full health. Perfect for Assassin’s that want to buff their damage output.
- Can be found on a dead gnome east of the fast travel point for the Underdark. (X:72 Y: -183)
- Phalar Aluve (Longsword)
- It is unique because it is a longsword that has the ‘finesse’ modifier, meaning it can sneak attack. It also has an interesting special action to buff allies, or debuff enemies.
- Found in the Underdark, stuck in a stone just outside of Selunite Fort. (X:119 Y:-191)
- Spidersilk Armor
- This light armor gives a +1 to stealth checks and gives a bonus to constitution saving throws. Perfect for the stealth aspect of this character and passing constitution checks for spell concentration.
- Can be found on
Minthara. She will be in the northeast corner of the Shattered Sanctum in the Goblin camp (X:-551, Y:231), but she will move depending on story choices.
- Boots of Striding
- Another excellent piece that gives momentum when casting a spell that requires concentration, which is quite a few of our spells in this build. Also gives +1 to Athletics and while concentrating, the wearer can’t be knocked prone or pushed.
- Note: These are medium armor boots and wearers cannot cast spells with them on, unless they have
Medium Armor Proficiency. That means you will need to forfeit the increase to charisma with the level 4 feat, and instead opt for 
Moderately Armoured. Also, Githyanki have the proficiency inherently if you chose one during character creation.
- Also found on Minthara.
- Springstep Boots
- A good alternative for those who don’t have Medium Armor Proficiency for the Boots of Striding. They provide Momentum for three turns after dashing, which happens often as a rogue with Cunning Action: Dash.
- Can be found in the Shattered Sanctum, behind Dror Ragzlin’s throne in the treasure area (X:-296, Y:74). The door can be opened by using Dror Ragzlin’s Key or picking the lock.
Strategy and Tactics
The main pull of this build is the devastating first and second round of attack when you successfully surprise a group of enemies. However, before the actual attack, you always want to prepare with this build to make it as inundating as possible. Let’s go over our pre-battle check list:
- Bind Pact Weapon – This is crucial! Before attacking, make sure that you have bound your held weapon. Annoyingly, you have to do this after every long break, but it lasts until you take another long break. This is the Warlock ability that makes your held weapon gain the proficiency bonus from your large Charisma stat.
- Short Rest – Warlocks really benefit from short rests because their spell slots are replenished. If you don’t have all your spell slots, make sure to take a short break before initiating combat.
Haste – You can buff your character with Haste before combat, if you have a magic wielder in the group that knows the spell. Alternatively, you could also use a Potion of Speed, but those are best saved for important fights.
As we mentioned in the summary at the beginning of the guide, it’s a pretty simple strategy: Sneak up, and surprise your enemies with a sneak attack, being sure to target the strongest foe who also hopefully has other enemies around them. The Assassin perk, Assassin’s Alacrity, will kick in and refund you your action points after you sneak attack and the battle starts.
Now, due to your character having high initiative with the Alert feat, you can attack the surprised (and already wounded) main foe that you originally targeted again. With them surprised, your next hits will be critical; the blows will also have a chance to cause that enemy and surrounding enemies to have to pass a wisdom saving throw or become Frightened because of your Warlock feature, Mortal Reminder.
Luckily, when enemies are Frightened, they can’t move, making them easy prey. You can either look for opportunities to blast them off ledges or cliffs with Eldritch Blast, or see if you can hide behind them and sneak attack some more. Another tactic might be to cast darkness on the enemy group, blinding them. This allows you to sneak attack them because you’re attacking with advantage and can see through the darkness with Devil’s Sight. After this sequence, the battle plays out normally, with the main difference being you have dictated how it is set up and crippled their forces by removing the main threats.
I am curious, what end game (Act 3) equipment is recommended for this build?
That’s a good question! There are so many options, but for the sneaky aspect of this build, probably the Bhaalist Armour paired with the Duellist’s Prerogative. For Helmet, the Birthright, and for gloves (if you’re using eldritch blast with the build), then the Quickspell gloves is an excellent choice. Does that help, or were there other equipment slots you had in mind?
Hey m8, thanks for the guide! Just have one question, the boots of striding are medium armor and wont let me cast spells? I dont have medium proficiency and your guide doesnt cover it?
cheers
Hello! I hope you’re liking the build so far. Sorry for that oversight with the boots. As I imagine you’re already well past character creation (otherwise you could’ve chosen a Githyanki), the easiest way will be to simply respec your character and choose the ‘Moderatley Armored’ feat at level four. You can make up the difference for charisma later on by using the Mirror of Loss or getting the Birthright Hat in Act 3. An alternative solution would be grabbing the Springstep Boots in Act 1. They have a similar effect that provides momentum for three turns upon dashing, which you’ll do more after class switching to rogue because then you’ll have Cunning Actions. I’ll make a note in the guide about this; thank you for pointing it out!