IIRC its either Shinryu or Omega that takes the cake of strongest thing that the WoL has fought without any outside interference (and even then omega gimps itself by turning into human form outside of savage which isn't canon). Everything else was either weakened or we had a power boost from something.


Even with the things we got help with, I don't think ultima counts because we were hella weak back then. I'd be tempted to throw my hat in for Alexander because we fight a gimped Alexander just trying to fulfill a bootstrap paradox, so an alexander just trying to kill you could probably just pull a "kill your mum" on you.

Obviously full power bahamut gets a special mention, but I seem to remember an interview saying shinryu was actually stronger, but I might be misremembering.