Crossover Stories: The Letdowns

This is inspired primarily by Alpharad's description of Jump Force as, "a game written by someone who knows a LOT about One Piece and not much else."

And I want to know: What crossovers underwhelmed you? Because the writers didn't have familiarity with the guest material, there was a complete screentime imbalance, the vague cloud of licensing and contracts caused problems, whatever reason.

My examples are niche, but: the Cartoon Network appearances in the show Jellystone where you start noticing how few of the CN characters get any dialogue, and you're just wondering if they just couldn't get more voice actors back.

Also this crossover was really random, so I don't know if it had potential TO waste, but after seeing the really good art previews for the upcoming DC/Sonic crossovers - I just remember that time Superman met Top Cat, who was drawn like this. I'm still confuzzled by it (and he was barely relevant to what happened in the story anyway).