Here is the full list of all 36 Garshasp: The Monster Slayer achievements.
Finish the game in normal mode
Execute 100 rage attacks
Execute 100 counter attacks
Kill Hitasp without getting hit
Finish the game in easy mode
Finish the game without using any health fountains
Find the sixteenth Hoom seed
Do not get hit while sliding down in Ooshidaran
Do not get hit while sliding down in Jungle
Do not get hit while sliding down in Siavoshgard
Finish the game in hard mode
Finish the game with no game overs
Finish the game without saving
Kill Hitasp
Hit 7 enemies with a rage attack
Fully upgrade the mace
Fully upgrade the sword and the mace
Upgrade the mace
Fully upgrade the sword
Achieve the dragon mace
Kill Gandarava, the Sea Monster
Kill Gandarava without getting hit
Kill Khishma
Kill both Viamboor without getting hit
Kill Viamboor without getting hit
Execute the first counter attack
Find the fourth Hoom seed
Throw ten enemies in the water of the lake while on the raft. (with a splash!)
Kill 300 Enemies
Kill both Viamboors
Execute the first rage attack
Slay Akatash
Upgrade the sword
Kill 100 Enemies
Find the first Hoom seed
Kill Viamboor