This challenging boss is found on the Moonlight Altar, in the Ringleader’s Evergaol. There’s some clear lore implications here, but suffice it to say that it’s quite interesting that the leader of the Black Knives is in an evergaol on what seems to be Ranni’s home turf. This boss has a ton of HP and some dangerous attacks, but is surprisingly straightforward to deal with once you’ve got the rhythm of the fight down.
Wearing one part of the Bell Bearing Hunter Armor (even just the gauntlets) will make your rolls interrupt the boss — this can make it easier to get out of range safely when rolling away from the boss.
Alecto is immune to all status effects except for Frostbite, so alter your loadout accordingly.
Additionally, the boss is resistant to all elemental damage, especially Holy damage. Many characters will benefit from switching to a purely physical affinity for their weapon while fighting this boss.
This boss does very long combos, so if you aren’t willing to take damage to deal damage, you should wait for one of the leaping attacks to miss, and then punish. The charged attack where Alecto drags her knife on the ground and then sweeps it upwards also has a very long recovery period and can be punished.
This boss can be backstabbed, parried, and staggered.
As always with these kinds of fights, I recommend that anyone who struggles with this fight equip a 100% Physical defense shield and hold block while walking backwards the whole fight. During some of the longer combos, you’ll need to roll, since otherwise you’ll run out of stamina and be staggered. Otherwise, as long as you’re letting go of block when Alecto backs off to recover stamina, you should be able to block most of what she throws at you. (Note that equipping a piece of the Briar Set that drops from Elemer can make your rolls safer.)
Wait for the boss to miss a leaping attack, a charged attack (where she drags her dagger on the ground), or the grab, and then punish with a jumping attack of your own, followed by a single light attack, followed by rolling away. (You can identify the special jumping attack by the fact that the boss’s knife will glow with red flame, but she’ll keep the knife low to the ground.)
While blocking is generally effective, know that the leaping/charged attacks, the grab, and the two magical attacks that this boss can do all cannot be safely blocked. However, the leaping and charged attacks can be avoided by rolling backwards twice (you can even just sprint away when you see the leap attacks starting). The magical projectile needs to be dodged by rolling sideways. The grab absolutely cannot be blocked, and you’ll take a ton of damage if you let it hit you. Fortunately, if you’re walking/rolling backwards the whole fight, this will usually miss.
The only time you’ll really be in danger from the grab is after attacking the boss — occasionally, she will dash sideways after getting up/recovering and immediately do the grab attack, in which case you’ll have to dodge roll it. If you want to avoid being in danger of eating this, don’t follow your jumping attack with a light attack, and don’t mindlessly roll after attacking, but instead wait until you see what the boss is doing — rolling early will ensure you eat the grab.
This strategy works the same with magic; your best time to punish the boss with spells or other ranged attacks is when the boss misses one of her leaping or charged attacks. You can also fling spells when the boss approaches, although the boss will generally dodge attacks unless she’s starting an attack animation. Fortunately, she is easily interrupted.
Once you get more comfortable recognizing the boss’s moves, you can also use light (or fast magic) attacks to punish the long thrust after blocking or dodging it:
If you feel up to it, put the shield away and start relying purely on rolls. An inbetween solution is to keep your shield out out but quickly two-hand your weapon when you’re preparing to do a jumping heavy attack — two-handing your weapon will allow you to stagger the boss and get some critical strikes in, making this fight go much faster.