>>56131761. Lava Lamp Room - Counter with freeze ray
2. Storm Room - Counter with Counter Hurricane Butterfly
3. Maintenance Tunnel -? Sink through the waves using a force-wall suit to avoid drowning. Follow the tunnel down to the land of the board-game goblins.
4. Board Game Goblins - Summon a fluffy baby owlbear for them to play with. Barring that, summon kittens instead.
5. Since we're on Floor 3, summon a noodle bridge to get us down to floor 2 in the room with the star.
6. Now swing down via noodles to the room above Sans.
7. Now swing down via noodles to the room in front of Sans.
8. Leave some milk and cookies for sleeping Sans as we roll out the final EXIT door at the bottom of the tower.
* We can get to the goblin room without breaking the 4th wall, but there's no clear alternative past that. I assume the room shuffler bit is a reverence to The Cube, so it might be plausible to stay in the storm room until it is moved, use the bomb to make a hole in the floors on the right, get into the moving room, and swap the and moving room with icy gunpowder room or something. Then politely ask Sans to move since we didn't murder everything down here, and bounce out. Some lateral thinking and liberty with the rules appears to be required though.