Use geo chains to get your hands on the boxes spread around the map, and use the boxes to make a tower to reach the monster. You'll need a Heavy Knight to throw high enough to reach boxes on the ledge.
Chapter 2: Grudgeful Memory
Use iron boxes so that you can throw the spare geo blocks next to a block of the same color for a chain to bring the thieves down.
Chapter 3: Student Chaos
The guide recommends a tower of 8 characters to reach the Silence block, and then move the silence block onto the yellow panels so the dragons can't use skills. Stay on the Blue panels to attack.
Chapter 3: Nightmare Days
Use throwing to have a character on top of each pedestal, and move the two Geo Blocks along as well, so the geo blocks are stacked on top of each other on the pedestal closest to the Majin. Throw a spell caster on top of the Geo Blocks, and use Star or something to attack the Majin.
Thanks, I beat it, though not by any means in that link. Trying to do that however did lead me to my strategy. Basically I used 3 monsters to bounce. Gotta be careful at the top though since if you throw the block and it isn't on a guy it'll get stuck there.