Zekke
Green Slime
This is a more major of a glitch than the other one. You can use blink to teleport past Rock in Mt. Bloom and skip to the gas-filled tunnels before the quest. Note, collecting the quest item before you are actually on the quest will leave you permanently stuck on the quest unless you reset Mt. Bloom with commands.
Note how I'm in this room before actually having the quest that lets me go here.