Boogey Tent is most vulnerable to Fire, so use that. It can cast PSI Flash α, which can make you cry uncontrollably or feel strange. If Ness has Healing β, he can fix those conditions, or if you have a recovery item, you can use that to cure those conditions.

Aside from weak physical attacks, Boogey Tent can increase its defense, use a Neutralizer, and spit Fly Honey to immobilize someone for a turn.

If you can afford Bottle Rockets from the arms dealer in Threed, you can use those against Boogey Tent. In the worst case, it would take 7 bottle rockets to defeat the tent if all of Ness and Paula's attacks missed (which is highly unlikely). In the best case, it would take fewer than 4 bottle rockets (assuming Ness and Paula hurt the tent a lot).

Once Boogey Tent is gone, you'll see that a couple of zombies are guarding a trash can. Look in the trash can to get the Fly Honey.