arena tips for defeating rebels/phoenix and empire

i play on ios so i wouldn't know how to reset the acc plus i dont wish too lol i mean i already got event characters such as mother talzin and all i win only sometimes in the arena but stuck 3000-4500ish for now i prob stick with nics advice for now but still any tips would be helpful other than re rolling all over again cause i did sign out try to re roll and my arena rank on that was still around 5000 so i don't think re rolling will help me today i did hit 2488 in the arena but went back to 2949 so SLOWLY getting there but still hard as there are 7* characters with insane power like around 50,000 60,000 while my power is 30,000.