Is there an unbeatable Pokemon team?

Yes. 5 Shedinjas and a Pokemon immune to flying moves. ALL lvl. 100

Edit*

Are you an idiot? There's no Pokemon immune to flying moves.

Also no unbeatable teams. Just very good ones.

Edit*

well I recon the best team would be a team of level 4 (hatched from egg) rattata - because an egg hatched ratata has the move endeavour and at level 4 it learns quick attack and with a focus sash. so there for;

first go - the higher level Pokemon will go first and use what ever move it does. the focus sash prevents 1 hit ko leaving 1 hp then you have a go and use endeavor reducing it to 1 hp

second go - you use quick attack (which ALWAYS goes first) and kill them

bam!! your Battle against ANY Pokemon lvl 100 or whatever is epically won!!

[no cheating is used]

EDIT: On the previous tactic is their Pokemon has quick attack or annything with a higher priority you are screwed... and if they switch out Pokemon... you are screwed...