Here is the full list of all 55 Iron Jaw achievements.
Defeat 300 enemies
Defeat 50 Ranged enemies
Defeat 50 poison melee enemies
Defeat 100 Melee enemies
Defeat 100 enemies
Defeat 50 Melee enemies
Defeat 50 enemies
Defeat 500 enemies
Defeat 1000 enemies
Defeat 50 Big enemies
Defeat 100 Big enemies
Defeat 300 Big enemies
Defeat 500 Big enemies
Defeat 1000 Big enemies
Defeat 50 Crabs
Defeat 100 Crabs
Defeat 300 Crabs
Defeat 500 Crabs
Defeat 1000 Crabs
Defeat 50 Explosive enemies
Defeat 100 Explosive enemies
Defeat 300 Explosive enemies
Defeat 500 Explosive enemies
Defeat 1000 Explosive enemies
Defeat 300 Melee enemies
Defeat 500 Melee enemies
Defeat 1000 Melee enemies
Defeat 50 poison enemies
Defeat 100 poison enemies
Defeat 300 poison enemies
Defeat 500 poison enemies
Defeat 1000 poison enemies
Defeat 100 poison melee enemies
Defeat 300 poison melee enemies
Defeat 500 poison melee enemies
Defeat 1000 poison melee enemies
Defeat 100 Ranged enemies
Defeat 300 Ranged enemies
Defeat 500 Ranged enemies
Defeat 1000 Ranged enemies
Defeat 50 Kill 50 Spawner enemiesenemies
Defeat 100 Spawner enemies
Defeat 300 Spawner enemies
Defeat 500 Spawner enemies
Kill 1000 Spawner enemies
Defeat your first boss
Defeat 3 Bosses
Defeat 10 Bosses
Defeat 50 Bosses
Defeat 100 Bosses
Pick 50 Power-Ups
Pick 100 Power-Ups
Pick 300 Power-Ups
Pick 500 Power-Ups
Pick 1000 Power-Ups