17. Marrymore
Outside
As soon as you arrive, head up-left to the inn.
Go to the second floor, go inside the room to the right and grab the frog coin from the hidden chest on top of the shelves directly above the door.
Go outside and head up-left to the church. Speak to anyone to trigger the cutscene.
Next, head to the right around the side of the church and take the hidden entrance behind the wall to the basement.
After helping the snifit bust down the door inside, take a safety save! The upcoming fight can easily go very badly.
Instead of "talking" to the door to trigger the cutscene with Bowser, leave the room after saving and immediately walk back in. This is faster than mashing through the text.
Break down the door with Bowser, then do the minigame where you catch each snifit and return the items to Booster. Remember that the final item (the crown) is on Booster's head!
Get a kiss from Peach, hopefully not Bowser or Booster or both, then get ready for ze cake...
Bundt
Phase One
Use regular attacks on the cake with all characters until it starts moving. The chefs' attacks are fairly easy to timed block.
After the cake moves the first time, use a Red Essence on Mario before attacking again. Then whack the cake once more, and begin phase two.
If your attacks are not timed properly and the candle phase doesn't start when Geno attacks, then defend with Mario and Bowser and attack again! The important thing is to start the second phase with Geno because it sets up the turn order so Bundt gets one less turn.
Phase Two (Blow those candles out!)
Use untimed attacks with everyone until all the candles are gone, then a final untimed attack to finish off the top section of the cake.
Each attack blows one candle out, regardless of the damage. When the cake attacks, it revives one candle. This is the most dangerous part of the fight.
If Bundt uses Sandstorm/Blizzard together, have someone use a Froggie Drink. Otherwise, try to just keep attacking and end this phase as fast as possible.
Bad RNG is Sand Storm, or multiple uses of it. Good RNG would be the Cake attacking Mario a lot while the Red Essence is active, or just Bowser. If you do get hit by Sand Storm, you generally want to just keep attacking anyway to get this phase over with as quickly as possible.
Phase Three
Have Mario use Jump every turn, while Geno and Bowser use regular attacks.
Use Pick Me Ups often when teammates get downed.
Bowser is a tank, and will last the longest, but Mario and Geno may die frequently.
In this phase, if Bundt uses Sandstorm, use an Able Juice on Mario only, and have Mario continue to use Jump.
Mario reaches level 6 - ATK (Learns Super Jump)
After The Fight
Head back outside of the church via the front door, then head southwest and leave Marrymore and head all the way back to the Mushroom Kingdom.