"It's not easy, but you have to be persistent. You might have to defeat a demon lord, or warp through several worlds. But once you do, you walk up the wizard stairs, and produce your magic key you got in the water world and unlock the chamber door. Then, you walk right up to the princess, and give her a smooch... Does that make sense?"

- The Lich King is a lord and can be described as a demonic zombie and he was defeated by Finn.

- Finn warped to Farmworld, the Citadel, the Time Room, and the Beyond the Grotto universe (can be the Water World?).

Now he can just walk up the wizard stairs (maybe he's gonna have some "wizard and magic" adventures or drama, in case the steps are the 3 wizard characteristics - magic, madness and sadness) and, somehow, make a key with the Sea Lard (or something from the Sea Lard) and surpass a barrier between the princess and him...

Does that make sense?