Here is the full list of all 40 I Hate Running Backwards achievements.
Kill the werebull
Destroy 50 watchtowers
Kill Scorpion King while two curses are active
Destroy a secret trash container
Kill the Lava Golem boss
Deflect 20 rockets
Gather 5k chunks from destruction
Kill Scrapjack boss
Kill the Scorpion King boss
Kill the Scorpion King before he burrows
Collect every powerup in one run
Die
Get the combo counter to x50
Destroy weapon crate
Finish a loop with all six curses active
Heal for 20 health during one session
Use ultimate ability 5 times in the same run
Deflect 500 projectiles
Detonate 50 explosive traps
Kill Scrapjack using only the hammer
Kill the biomechanoid without being hit
Kill Biomechanoid boss
Kill 1000 enemies with a hammer
Finish a game loop
Kill Ugh Zan without taking any damage
Finish a loop without receiving damage
Knockback 100 enemies
Deflect 50 cannonballs
Kill 10 RoadBulls on the Road ground
Destroy 30 mines while invulnerable
Gather 50k chunks from destruction
Kill the second form of Ugh Zhan boss
Get to the Scorpion king using only the hammer
Freeze 100 enemies
Kill Ugh Zan boss
Unlock 15 special weapons
Kill Biomechanoid while four curses are active
Destroy a special crystal in the Crystal cave
Collect 666 souls
Finish a loop without receiving damage with all six curses active