Bloomsday (known in the game's PAL version as Scumflower) is the fourth boss of Wario Land: Shake It! It can be fought in the boss level of Jiggle Jungle known as Bloomsday Blowout (Scumflower Skirmish in the PAL version). It is a giant potted plant that uses its petals as a powerful fan to inhale a large amount of air and release it as powerful strong wind.

The boss battle takes place atop a log in the middle of a lake. Bloomsday will attempt to blow Wario to the edge of the log where a Venus Guytrap waits to attack him. It can also spit out Bumbleprods, Flipstings or Bandineros, which Wario can use to throw at Bloomsday, temporarily stunning it. While it is stunned Wario can charge towards it, causing it to move closer to edge of the log. Bloomsday can also summon numerous thorny vines that will rise from the ground to attack Wario. It will continue to repeat these moves until it has been attacked at least two or three times, at which point it will change strategies. It will Ground Pound, causing two large thorny vines to appear and trap Wario in between them. The attack may stun Wario if he doesn't jump right before it hits. Bloomsday will then spit out a Boomdinero and then two Bumbleprods to attack Wario. Bloomsday can also try to suck and blow Wario towards the thorns causing him to let go of the Bandinero, but if Wario manages to resist the attack and dodge the two Bumbleprods, Bloomsday will Ground Pound again causing the thorny vines to disappear. This gives Wario a chance to attack with the Bandinero and attack Bloomsday. Once Wario does this twice he will push Bloomsday off the log, earning his fourth boss emblem.