The party's named scouting maneuver — a magical peephole in a door to eye a boss room before committing to a fight.
'Peeping Mongo' is one of the party's named coordinated 'moves,' a scouting maneuver in which a small magical hole materializes in a door so Carl can peer through and assess a boss chamber before triggering a fight — deciding whether Princess Donut's Clockwork Triplicate Mongos are even needed. Carl insists on calling it 'Peeping Tom' (so he can look first); Donut pedantically corrects him that they agreed on 'Peeping Mongo,' fretting that his mangling of move-names will cost extra training time. It proves its worth at the sandcastle's boss door, letting Carl spot Ghazi watching cartoons and abort a straight assault in favor of the Astral Paw provocation that exposes the Sand Ooze.
The party's boss-room reconnaissance move — peephole scouting before committing to combat.