-To kill a Bulborb quickly, have 95 or more Pikmin with you. Go behind it and press the C-Stick to attack him. It will be dead in five seconds if all your Pikmin charge him.
-You can kill the big Bulborbs by getting two Yellow Pikmin with bombs. Put them near it and walk behind the frog to wake it up. Quickly run away and it will go for the Pikmin carrying bombs. It will eat the bomb rocks and die.