You only fight creepers inside if you get the answer wrong, but more importantly, you must use the unit types in your favor with the new combat system. If you are going to fight in a plant dungeon, why not use as much fire as you can on your team? Fire both resist plant attacks and is super effective against them.
At this point of the game you have two great fire summons in the Orc defender and the Burning Zarish(fire cat boss), you also have a few summons with fire skills like the sunflower and the goblin lord. Since you are a mage you have also a lot of good fire spells to use, if you look at the description there is also fire skills that remove regeneration from the target which is great against the final boss of the dungeon.