Cool! Welcome aboard!
I've had the idea of using a water gimmick similar to the one used in this level, with exception of the Fishin' Boo. So, the player would hit the switches scattered around the room to control the water level and, in conjunction with slightly more complex obstacle setups and creative usage of floating platforms, make up for some challenge while not being too difficult or unfair. But... my ghost house level used an specific uberASM code to handle layer 2 water, and I don't know if you're familiar with that in order to apply the same effect to level 10... so you don't need to strictly follow my ideas. But if you do want to do it, and need assistance, feel free to PM me.
Regarding tileset, the regular castle tileset will do, along with SMW's level 101 BG, and a blue back area color. You can leave an empty boss room at the end as a placeholder for a custom boss. The base ROM has a debug feature so Start+Select will beat the level.
I've had the idea of using a water gimmick similar to the one used in this level, with exception of the Fishin' Boo. So, the player would hit the switches scattered around the room to control the water level and, in conjunction with slightly more complex obstacle setups and creative usage of floating platforms, make up for some challenge while not being too difficult or unfair. But... my ghost house level used an specific uberASM code to handle layer 2 water, and I don't know if you're familiar with that in order to apply the same effect to level 10... so you don't need to strictly follow my ideas. But if you do want to do it, and need assistance, feel free to PM me.
Regarding tileset, the regular castle tileset will do, along with SMW's level 101 BG, and a blue back area color. You can leave an empty boss room at the end as a placeholder for a custom boss. The base ROM has a debug feature so Start+Select will beat the level.