Billy can see who the descendants of past Champions are. This opened up a new world for him.
Past Champion: Billy! My great-great(×10)-granddaughter is there!
Billy turns his head and sees a little old lady crossing the street.
Past Champion: Go help her!
Billy helps her home while listening to stories about her grandchildren. Past Champion chirps happily while the others grumble.
Then Billy joins the League. He holds back a surprised yelp when he sees the aura around Barry, Victor, and freaking Bruce Wayne!! The Champions scream like little girls when they see their descendant defeat a villain.
Bruce's Grandfather: Look at my grandson! He took them all!!
Barry's Grandfather: No, look at my grandson! He's faster than anyone!
Victor's Grandfather: I know my grandson is better than all of you idiots.
Bruce's Grandfather: Now I know who he takes after.
And it's constant. Day and night, the Champions in Billy's head tell him about their grandchildren. Billy is honestly tired of it. Moreover, the Champions' memories have slowly penetrated his memory, so he sometimes begins to confuse the past with the present.
Marvel: *looks very closely at the puzzle that will open a portal to the world of chocolate bunnies*
Batman: Are you going to look at this for long?
Marvel: *waves it off* Borkut, daddy's busy, go play with your brothers.
Batman: *blinks in shock and looks at Captain* But...
Marvel: Dad's working, I promise to take you to Aunt Hestia tomorrow. Let me work, son.
Batman: *steps aside*
Marvel: *nods in satisfaction*
Also, the memories bring up emotions that Billy can't hide.
Marvel: *looks out the window at Earth with a sad expression*
Superman: Marvel? Is everything okay?
Marvel: *has a memory in his head of when one of the past Champions was married to a very powerful sorceress. They often flew around the Earth. The wife looked very beautiful in the rays of the sun*
Marvel: I think I miss my wife.
Clark doesn't know how to react to this statement. Did Marvel have a wife? Was he married? Clark didn't know what to say to Marvel at that moment, so he just stood there in silent support.
Billy ended up becoming more of a parental figure to some of the heroes.
One day, Zatanna walks into the Watchtower and sees Marvel.
Zatanna: G-g-grandpa?!
Marvel: Zatanna! *hugs her and starts spinning her* Grandpa missed you! Oh my god! You have your grandma's eyes!
The League was on the sidelines, picking up their jaws.