In this video guide I will show you how to defeat the Ent. Now this can be one of two boss fights at the beginning of the game. Either it will be Singe or Ent. Each has a different room to fight in, so you will know if you have fought Singe that this one looks different.
The fight is pretty basic. He has a stomp that creates a shock wave at you for starters. Then when you damage him enough he will shoot poison orbs at you. Make sure you pause a second then roll to dodge them. At a points he will summon minions during the fight as all other bosses do. His critical spot is on is back for extra damage.
Either kill him by shooting him in the head for the shotgun, or kill him by shooting him in the legs for the maul. Once he is dead the achievement will pop.