Entering and leaving your Serenitea Pot using the physical item instead of teleporting using the map. Have someone join your world. A co-op version of your world will load and the boss will respawn (and it might have enough time to respawn in the "real" version of your world once you exit Co-Op.
If you're worried about it, when you're at your next gate, just stall your progress and build your characters as much as possible. At worst, you'll end up jumping an extra World Level and have some rougher stuff ahead of you, but you can take as long as you need at your next wall also.I know, but I think they all be like that imo . 66 27 93 227 73 26 70 370 4