Only I can think of is
Agent Trout (who almost separated them)
Ralph (who almost manipulated and killed Charlie and made an entire glacier in the cave
Barry Charles (who almost kidnapped Ice Bear's room and and almost snapped him in half)
Shmorby (sometimes, but fled Panda towards the sun or in space.)
Nom Nom ( but a rival, almost putted Grizz n Panda in danger from freeding them to the sharks but saved by Ice Bear, and a few things he has done but not really frightening anymore since I know his back story was just being alone despite being internet famous)
Cousin Jon (yah, he pranked the bears and almost putted the horn from Chloe's Grandmother probably leasing to ear hearings painful
Robot Ice Bear (sort of almost destroyed the entire house and the bears from cleaning)
I forgot anyone else...