Counter Tips

If the BJ used the Mecha-Koopa, use Rebel's Guard to absorb it, then wait till your opponent tries to punish you and release Rebel's Guard and do the little AOE burst. I like to follow it up w/ a grab

If your opponent recovers high and tries to cover their recovery with the Mecha-Koopa, use the Grappling Hook to grab it

If your opponent tries to zone you out w/ the cannonball and Mecha-Koopas, farm for Arsene then counter zone w/ Eigaon.

Respect Bowser Jr. at lower percents, especially if you don't have Arsene. There's no coming back if you get fair train'd off