#2. CM Punk made some independent appearances in 2015 and 2016
Before joining WWE, CM Punk was a hugely popular star on the independent wrestling scene around the world. He became so popular that when making his debut on WWE television for ECW, the whole crowd in the Hammerstein Ballroom was chanting his name.
Punk seemingly made a return to the independent scene, disguised, a year after his WWE departure. Firstly, in 2015, he made an unannounced appearance managing Japanese wrestler Kikutaro. The match took place at Freelance Wrestling, with CM Punk draped in a cloak.
Secondly, in 2016, CM Punk interfered in a match, with a masked disguise, helping friend Ace Steel, delivering a GTS to his opponent. The promotion's owner, Silas Young, confirmed it was Punk under the mask that night, though Punk never confirmed whether it was him or not.
Silas Young confirmed it was CM Punk with Fightful:
"I had Dave Prazak and Ace Steel booked on the show who are good friends with Punk. My wife came up and said ‘Punk’s going to do a run-in-on the match, do you mind?’ I said ‘of course I don’t mind.’ This is ten minutes before the show, not something I booked. That’s how it happened. I think it’s because his buddies were booked on the show. Just a kind of circumstance and luck based on who I had booked that it worked out the way it did. I never saw Punk at the building. Can I 100 percent confirm it was him? No. I can say I’m 99.9% certain it was him. It’s a cool thing for the area and the promotion," Silas Young said. (h/t 411Mania)
Many speculated that Punk had got the itch once again, but nothing ever materialized beyond these appearances.