Japanese Name: Split Mushroom (same)
"He occupies the laboratory and will attack whoever visits there"
Weakness: Lightning Web/Raijingeki
Obtain: Soul Body/Kuuenbu (and Kuuenzan)
Split Mushroom is a very easy battle if you've already defeated Web Spider (you should have, at least). With X, just keep attacking him with Lightning Web and it will interrupt all of his attacks. With Zero, you have to attack while he's on the ground and be careful because Raijingeki because the attack animation is quite slow. To make it easier, just start the attack before he starts moving and you'll have no problem. When he's creating the holographic clones just destroy them with Raijingeki as they're created. He should be down in no time, giving you Soul Body for X and Kuuenbu/Kuuenzan for Zero.