Here is the full list of all 28 Tallowmere achievements.
Make it to Room 20 without sacrificing any kittens.
Acquire a 7-star piece of headgear without sacrificing any kittens.
Acquire a 6-star piece of headgear without sacrificing any kittens.
Acquire a 5-star piece of headgear without sacrificing any kittens.
Acquire a 6-star outfit without sacrificing any kittens.
Acquire a 5-star shield without sacrificing any kittens.
Acquire a 7-star weapon without sacrificing any kittens.
Acquire a 5-star outfit without sacrificing any kittens.
Defeat the three-headed Hydra without sacrificing any kittens.
Return the flag without dropping it, and without sacrificing any kittens.
Defeat Jazza without sacrificing any kittens.
Blow yourself up with a rocket launcher.
Make it to Room 10 without sacrificing any kittens.
Acquire a 5-star weapon without sacrificing any kittens.
Free Lady T from her peril without sacrificing any kittens.
While stealthed with the Emerald Dagger, stab an enemy in the back.
Receive healing from Lady Tallowmere while on 1 health.
Return the cursed flag to Lady Tallowmere without sacrificing any kittens.
Kill yourself using your own grenades.
Sacrifice all nine kittens and die a little inside.
Make it to Room 30 without sacrificing any kittens.
Make it to Room 40 without sacrificing any kittens.
Make it to Room 50 without sacrificing any kittens.
Make it to Room 60 without sacrificing any kittens.
Acquire a 6-star weapon without sacrificing any kittens.
Acquire a 6-star shield without sacrificing any kittens.
Acquire a 7-star shield without sacrificing any kittens.
Acquire a 7-star outfit without sacrificing any kittens.