Here is the full list of all 55 Yaga achievements.
The base game contains 42 achievements, and there is 1 DLC pack containing 13 achievements.
Give the Golden Apple to the Tzar
Skip a carefully crafted cutscene
Become a royal advisor
Reach the end of the game
Finish the game without forging any tools
Spare an old enemy
Lock Koschei up
Crazed man + Poludnica = Love
Help Morozko find love
Help the vodnik live in peace
Call in a spared creature to help you
Give the Muddy Water of Youth to the Tzar
Turn a sickle into a weapon
Be really Righteous
Dig up a burried treasure
Give the Gilded Apple to the Tzar
Trick the polevik's minions
Lose an arm!
Attack all old altars
Kill village chickens
Hit the church bell
Remain a blacksmith
Be foolish
Marry a warrior queen
Become the Tzar alone
Witness Yaga's facepalm
Try to flirt a few times
Let Koschei go
Kill an old enemy
Destroy Morozko's Heart
Be really Aggressive
Be really Neutral
Be really Foolish
Be really Greedy
Ivan + Poludnica = Love
Polevik + Poludnica = Love
Make the priest rich
Throw a few enemies away
Attach a cartwheel to your arm stump
Use the chainfork to pull a few enemies closer
Make the vodnik rest in peace
Give the Water of Youth to the Tzar
Help Kuma Lisa eat Oakvale's chickens
Take the Stuhacs' offer instead of the Magic Ore
Steal the Magic Ore without getting caught
Complete the Loan Shark story arc
Collect all the Trinket Kid's toys
Rescue the Vodnik Mother's kids