Here is my 100% Achievement guide for Mochi Mochi Boy!
You have two modes to choose from - Tower & Dungeon. Obviously pick Dungoen mode.
The first level will be the exact same everytime, but the second level will be random and different.
So you can either just keep restarting until you get an easier second level or just have a think, take your time because generally, the second level isn't hard at all anyway.
Thats all you have to do to unlock this achievement!
Hope this helps!