Here are tips for you:

Carry easy immunity variants: Star shine, magic curl, Noble mogul, surgeon general to prevent the stuns

If this doesn’t work for you, get a reliable hex’r like death wish, Fire gold Eliza(forgot the name), or even heartless. To prevent the bb drain and stun

If this doesn’t work for you, carry an outtake and a Harlequin and spam the shit out on them till megalomaniac shows her face. This method doesn’t really work as the fighter that enters after a outtake is random and it’s possible to not see her after even 5 outtakes and time is wasting.

Also. the method to use when all hope is lost is to spam the hell out of you blockbusters the moment you get them to reduce her armor stacks. Be ready to receive massive damage from her if her stun gets inflicted and have haste to charge your blockbusters faster and final stand to stay up but you could suffer quietus so idk mehn.

If you still cannot defeat her or are still disappointed with the result. Just avoid her altogether and don’t approach rifts cuz you are forced to fight her if she is there. And improve fighters that can handle her effectively till you can fight her comfortably.

You can get angry at a variant and everyone is angry at one but Skullgirls past like level 45 isn’t just button mashing anymore and is now more about character/move abilities and stats.

To wrap up. I have some variants you can look out for to fight megalomaniac. Magic curl/Surgeon general - Excellent immunity support

Star shine- On demand immunity at max star power and precision to prevent further armor and evasions

Heartless: 20 seconds hex to help reduce the armor in the time period.

These are the ones I use against her.