The Pirabbid Plant is the first mid-boss in Mario + Rabbids Kingdom Battle, providing the first real challenge as its a enemy with a huge power and health rating in comparison to regular foes. Spawny accidentally creates him after fusing a normal rabbid with a piranha plant. And it's all Luigi's fault.
You still have to deal with regular enemies on the field. My strategy was to hide on the top levels and pick off his health slowly. Though his fire breath is something to watch out for.
Out all the sub-bosses, he was by far the easiest. With weak weapons and powers early in the game, you do have to be patient.
But he will fall and defuse into normal enemies.