Bob-ulks are massive purple Bob-ombs that first appeared in Paper Mario: The Thousand-Year Door. Bob-ulks are the strongest Bob-omb sub-species in the game. Their attack method is to charge first themselves and explode after a few turns. However, if there's another explosion, they'll also explode immediately. When exploding, it causes a lot of damage, even more than Bulky Bob-ombs.
Bulky Bob-ombs are weaker than Bob-ulks, making the Bob-ulks the strongest. Oddly, Bob-ulks are a bit smaller than Bulky Bob-ombs, although they cause much more damage.