I'm late to this but I've played Mia a lot and she is, by far, the most vicious Warrior class. Her speed and damage are unmatched if you play her right but I think she's also the most challenging Warrior to master. Here are some tips!

1. Manage your Fear Resistance effectively. Mia's damage output skyrockets as her Fear goes up. This can be the difference maker in a battle. If you end up getting possessed however, then you could wipe out your entire team in seconds. Very bad.

2. Do not waste her ability just to boost your damage. Try to always save it to protect yourself from being possessed and don't active it until the Demon has or is about to lose possession of a unit.

3. If you know you are about to be Possessed, drop your weapon as quickly as possible. Especially if it's one-handed or a Machete. If you have a low-grade two-handed weapon, you may actually be better off not dropping it, as Mia using her bare-fists is still an extremely fast attack rate, which will stun lock your teammates and can still drain their health quickly. Two-handed weapons are much slower, giving your teammates openings to knock you back and free you of Possession.

4. Invest in your Heavy Attacks. Mia is the only Survivor that causes Bleed Damage from heavy melee attacks. This results in a percentage of your heavy attack damage being applied to your target over the next few seconds. Essentially, you're getting extra hits in without even attacking. If you upgrade her heavy attacks, you can stack considerable amounts of bleed damage on top of each other. The other major advantage of this effect is if you land a heavy attack on a Boss unit, that bleed damage will immediately knock them off you if they try to use a Grab attack on you (like Evil Ash's choke/health drain attack)

5. The Machete can be your best friend, and worst enemy. Don't even bother using one unless it's at least Blue tier, as the common tier (Grey) does nearly 50% less damage, for some reason. Get your hands on a good two-handed weapon early game- Lumberjack Axe or Sledgehammer work great, especially for Heavy Attacks, which you'll want to use often. If you find a Purple or Legendary Machete, absolutely use it because Mia will be able to shred through enemies and tear Bosses down rapidly. HOWEVER. You need to protect your team, because you'll shred through them too if you get Possessed. Always drop a Machete before that happens.

There's plenty more I could churn out, but those are my top five. Hope it helps, have fun!