Challengers of the Unknown #48) has our heroes battling Multi-man and the Challenger-Haters.
called "The Haters" here, in March of 1966.
it also features yet another version of Atlantis, which by my count has to mean there were at least seven different versions floating about Earth 1 in the 50s and 60s.
it's a good story, one I wish would have been completely included in the recent Doom Patrol Showcase v. 2. we only get the DP stories, and not the Challengers one. nor do we get the BNB team up with the Flash, but that's a different story for a different column.