From SmashWiki, the Super Smash Bros. wiki
Owen's Smash Tip No. 5: Event matches offer a variety of different scenarios that borrow inspiration from a bunch of video game series. In Super Smash Bros. for Wii U, if you have any item equipment on one of your custom characters, it will not be available for use in an event. Why? I don't know! Likely because they don't want you to bypass some event objectives very easily.

Hey, guys! I'm Smashbrosfan99. I'm a user on the SmashWiki. I don't contribute that often, but when I do, I usually help to improve the articles on this site. I don't play Smash competitively, however, I do enjoy getting the opportunity to play every once in a while. I'll expand this user page when I get the chance to do it.