The Time Devourer isn't that hard to successfully use the Chrono Cross on. It just takes fucking forever. You just need to be sure you've got a really even balance of every type of element available. You don't want to go in with a ton of greens and one red.
Beating that first Lavos isn't hard either if you're doing a New Game +. I've done it plenty of times on a + game.
Shit, Jess, I didn't even think to use Fire Rings against Omega. He'd always kill me with that fucking Atom Ray (or whatever the hell it was called) before I'd get a single shot in. Now I feel retarded.
I've also heard that Shinryu from FF5 is a pretty nasty boss. I never tried, though, because apparently the only weapon that does decent damage to him is the Dragon Lance, and I never found one of them. I tried stealing them from those Crystal Dragons for an hour or two and I kept getting shafted.