Get Crono killed.
Get Epoch with Wings.
then you ..
go to 2300 A.D. and have Robo lead your party. And then head to Geno Dome.
Then ride the conveyor belt. Kill the monsters with lightning 2 with Magus. (he can't do it at the start, but eventually, he'll OHKO the group of mobs)
Then go back the chute to the start. And repeat.