M is one of my favorite allies from the Magneto hero pack. Abilities aside, she provides acceptable value from thwarting 3 times then blocking. Her Enters Play ability is similar to Valkyrie, killing a 3 health or less minion in play (even bypassing Tough statuses). Although it won't always have a target, I love having this ability within my toolbox of allies for cards like Make the Call, Cerebro, or Call for Backup that always help us find the perfect ally for the moment. If we can upgrade her hp with Uncanny X-Men or Team Training (cards that are totally fine to play on their own), she can take out even bigger minions!

The 3 ATK stat also presents some interesting possibilities. It's probably worse on average than 2 ATK with only 1 consequential damage, but effects like Teamwork or Mass Attack that ignore the consequential damage will benefit from her. She can also use it on her last hp where the second consequential damage isn't as awkward, or it can be a tempo boost when needed if you need to prioritize that over efficiency.

Lastly, M has two great traits: Psionic and X-Men. She's a fantastic hit for "To Me, My X-Men!", turns Cerebro into a full-deck search, can be played by Psionic decks using The Power of the Mind and Psimitar, and has the many benefits of being an X-Men. Maybe not quite a staple-level card due to the abundance of great allies and need to have a minion in play, but extremely strong, especially in Trait-focused decks.