Highly effective Regeneration Tank for Karlach. (If used for Tav I recommend the Gnome race to get advantage on Wisdom Saving Throws).
This build focuses on the early Act 1 weapon, Shattered Flail. There are 2 key aspect to the Shattered Flail, the first is for each instance the weapon deals damage the user is healed 1d6 hp, the second is if you dont deal damage with the Mace you must make a DC10 Wisdom Saving Throw or go Mad.
Periapt of Wound Closure helps buff the first aspect by always getting the maximum healed amount possible (6 hp). Tiger Barbarian allows not only debuffs like Bleed and Reverb from Boots but it also allows Diadem of Arcane Synergy to activate granting additional damage. Tiger Barbarian gets access to the special attack Tigers Bloodlust which acts as a Cleave attack targeting upto 3 targets in a cone to deal damage. The Shattered Flail will heal off each enemy hit meaning a single attack will heal 18 hp. An additional synergy found in Act 3 is the Ring of Regeneration, since its paired with Periapt of Wound Closer it will always heal its maximum of 4 hp at the start of the turn. Fighters Class Action Second Wind will also heal its maximum amount of 14 hp.
To help offset the second aspect of the Shattered Flail you will need a significant investment into Wisdom to help ensure you never have a chance to go Mad (DC10 Wisdom Saving Throw). On this aspect taking your first Feat as Resiliant: Wisdom will help by bumping up Wisdom from 17 -> 18 granting you and additional +1 to Wisdom Saving Throws and adding your Proficiency Bonus to Wisdom Saving Throws (2-4 bonus). This is where the Diadem of Arcane Synergy comes into play. Instead of only having 18 in a stat for saving throws once you inflict a condition on an enemy you will get +4 bonus damage to Weapon Attacks. There is one key draw back. The only way for the Diadem of Arcane Synergy to recognize your Wisdom stat is if the LAST subclasses taken scales with Wisdom. In this case you will need to respec every level (preferably only after you get the Feral Instinct Feature at level 7) to have 1 War Cleric (or your choice of single level Wisdom class) after getting the Diadem. Other options include a single level in Monk as it provides 2 higher AC and the ability to BA punch after a Shattered Flail hit, tho do note that this doesn’t count for avoiding Madness in the early levels.
More synergies for Tiger Barbarian, Bleeding, and Reverb. Taking the Animal Aspect: Wolverine makes your Weapon Attacks against Bleeding or Poisoned targets inflict Maim status effect which completely removes the targets ability to move at all during their next turn & also forces Disadvantage on Dexterity Saving Throws. An additional synergy to this aspect comes from the Fighter subclass Battle Master. The special maneuver Tripping Attack has a chance to knock the target Prone. Prone targets must use movement to get up on their turn but thanks to Maim that target does not have any movement meaning their next turn is entirely skipped, the target cannot do any; Action, Bonus Action, Reaction, or move from the floor.
Additional Note: Try playing this build with a Paladin with Aura of Protection. An extra bonus to the Wisdom Saving Throw ensures anything greater then rolling a 1 will save from becoming Mad under the assumption you dont have +4 Proficiency Bonus yet or get inflicted with a debuff that lowers your Wisdom Saving Throw. Once fully built you should have at most a 5% chance to go Mad this is where Gnomish Cunning would come into play effectively making it impossible to ever go Mad.
