SpongeBob SquarePants: The Cosmic Shake

The Big Jelly is the large enemy with the bath tub. The baby boom is the one that shoots projectiles at you. I unlocked this quite easily in the Pirate Goo Lagoon world at the Scurvy Swamp checkpoint. From the checkpoint, jump below and go left. Take the bubble surfboard across a sunken pirate ship and then follow the next path. You will come upon a bunch of enemies, including the ones needed for this achievement. Just dispatch the smaller enemies and then stand between the Baby Boom and Big Jelly so the projectile kills the Big Jelly.
Side note: This is also a great spot to farm the Wrath-Tub achievement for defeating 25 enemies with the big jellies attack (I’d recommend taling out the Baby Boom first if going for the Wrath-Tub achievement here as the projectile will kill the smaller enemies before the Big Jelly can if not)

The Big Jelly is the large enemy with the bath tub. The baby boom is the one that shoots projectiles at you. I unlocked this quite easily in the Pirate Goo Lagoon world at the Scurvy Swamp checkpoint. From the checkpoint, jump below and go left. Take the bubble surfboard across a sunken pirate ship and then follow the next path. You will come upon a bunch of enemies, including the ones needed for this achievement. Just dispatch the smaller enemies and then stand between the Baby Boom and Big Jelly so the projectile kills the Big Jelly.
Side note: This is also a great spot to farm the Wrath-Tub achievement for defeating 25 enemies with the big jellies attack (I’d recommend taling out the Baby Boom first if going for the Wrath-Tub achievement here as the projectile will kill the smaller enemies before the Big Jelly can if not)