I never finished the original red/blue rescue team because I would burn out on the later dungeons that had lots of floors.
However this time I persevered through the 99 floor dungeons and got to Meteor Cave, and the Deoxys fight is really something else. I was normally able to cheese the previous bosses somewhat with thunderwave spam, but since there's 4 of them it was a lot more difficult to achieve that. I ended up keeping one of the clones alive and just spamming thunderwave on the main one to stop it using recover, but even that took ages because of light screen and cosmic power.
I think to date it's the only boss fight I've had to use a max elixir in.