Here is the full list of all 32 Hellbound achievements.
Play (and die) in a survival arena
Complete a campaign level in 300%
Kill a total of 1000 enemies
Die by a Hell Knight Guard
Die by lava
Check the entire credits
Finish the campaign
Kill Ferlord
Pick up a Soul Orb
Die by an Exploding Pumpkin
Kill 10 enemies with the Indolora without releasing the trigger
Pickup 100% of items in a campaign level
Pick up the Rocket Launcher
Kill a Pygon using the Head Crusher
Press the interact button and miss 12 times in a row
Find 100% of secrets in a camapain level
Kill 3 enemies (or more) with a single shot of the Triple Shotgun
Beat campaign level 1
Kill 100% of enemies in a campaign level
Find a secret area
Kill an enemy and drop its body into the lava
Find the super secret area in The Heroes' Cemetery
Find the "You got stuck" message in Flying Souls
Find the developers message in The Core
Complete all campaign levels in 300%
Beat a campaign PAR time
Finish the campaign in Old School difficulty
Finish the campaign in HELLMARE! difficulty
Get to the final wave in a survival arena
Survive more than 15 minutes in a survival arena
Kill 5 enemies (or more) with a single rocket or grenade of the Rocket Launcher
Kill 30 enemies during Hell Damage