Ladida Plains 1-6
From the Super Mario Wiki
The level starts with the player needing to stretch platforms below Princess Peach to throw her higher in the air and onto above platforms. At the end of this section is a ring that will teleport the player to the boss area with Boss P. Plant.
Boss P. Plant attacks by spitting Nipper Plants at the player and sending shockwaves at them. The player needs to use the Gloom vibe on one of the plants in the arena, climb onto it, and use it again when Boss P. Plant opens its mouth, before hitting his belly. After the third hit, Boss P. Plant becomes mad and starts jumping around the arena and sending out two shockwaves. After two more hits, the player wins the battle and frees the Toad that Boss P. Plant had swallowed.