Mortal Shell: Enhanced Edition

As stated in the description, this unlocks once you've got each of the three shades for the five shells and the Foundling. These shells have extra benefits once applied.

Each shell's requirements are:
Kill x(number) of (enemy name) as (shell)
Kill (miniboss) 5 times as (shell)/ Hadern has to kill 10 minibosses and Tiel has to kill his boss 3 times.
Complete a cycle as (shell)

Harros:
Kill 60 Brigands - These are the goons you'll find throughout the main map of Fallgrim and occasionally replaced inside the three temples. It's entirely possible to get this in your first run as Harros.
Kill Vim 5 times - Vim is the dual-wielding miniboss within the Shrine of Ash. You are guaranteed one of the required bosses for each shell but may get lucky enough for another to spawn in the same cycle. Grind Seeds - 888238 (kudos to Deathproof4289), 767553
Complete a cycle as Harros - Self Explanatory

Solomon:
Kill 40 Nocteserpers - These are the ghoul-looking enemies that keep trying to tear your throat out. From my own runs, they seem to spawn on any map. Grind Seed - 195573
Kill Ven Noctivagu 5 times - Ven spawns in the cave located between the Bat Tree and the Martyr's Crypt. This is the cave where Tiel's shell is found in the main game. Grind Seed - 664561
Complete a cycle as Solomon - Self Explanatory

Eredrim:
Kill 20 Faceless Cleriks - These are the hammer-wielding guys in the Seat of Infinity. One might spawn outside of the temple but don't count on that.
Kill Grisha 5 times - Grisha is the cave troll with blades for arms that spawns in the cave next to Fallgrim Tower. Grind Seed - 195573
Complete a cycle as Eredrim- Self Explanatory

Tiel (Both of his tasks have the same seed - 664561):
Kill 40 Slavers of Scorn - These are the enemies with swords poking out of them (and throw their head at you when on low health). They're mainly found in Martyr's.
Kill Enlsaved Grisha 3 times - EG is unmissable as you have to kill it to progress in the Crypt. You can combine this with killing the 40 Slavers.
Complete a cycle as Tiel - Self Explanatory

Hadern:
Kill 100 Enemies - Self Explanatory
Kill 10 minibosses - There are a minimum of five minibosses in each run. Vim, Grisha, Enslaved Grisha, Ven Noctivagu, and Evil Baghead (he's at the same camp as his normal location in the main game). Like earlier, you can get lucky and have multiple minibosses spawn in the same cycle. You can also use one of the earlier seeds to farm this out.
Complete a cycle as Hadern - Self Explanatory

Foundling:
Reach the first temple - Self Explanatory
Reach the second temple - Self Explanatory
Complete a cycle as the Foundling - Self Explanatory