This file details some considerations to make for a Mission build, and may eventually contain a few Mission builds from different playthroughs. We'll see how far I take it.
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Mission Vao.
Twi'lek teenager, lotsa skills and attitude, okay-ish on Taris then probably don't use her much once you get Jedi in the party, right?
Wrong.
Mission is the strongest companion. Seriously. Okay, not for all main character builds and not for all playthrough styles. She needs some support and some synergy, and for some playthroughs you are probably better off putting her in timeout on the Hawk where she can think about not sassing her elders while they're trying to save the galaxy.
But if your main character happens to start as a Scoundrel, or if you just happen to do a lot of stunning, watch out! This adolescent orphan can put everyone but the main character to shame.
Mission is the most flexible non-Jedi companion in terms of how she can be built. But she really does have to be built and used correctly to see her many benefits. Want a burst damager dealer who can help the main character trigger Sneak Attack damage? Mission is your girl. Want a reliable ranged damage dealer who can giggle at enemies while their health bar steadily declines? Mission won't break a nail. Want an elusive tank who can make funny faces at enemies while they flail about trying to land a blow? Mission won't even mess up her eye shadow. Want someone who can ACTUALLY handle skills while STILL being useful in combat? Move over, T3, Mission will do it with one hand while taking selfies with the other.
Thing is, she can pretty much only do ONE of those things in any given playthrough. And to get the full benefit, you may need to do a little more management than, for example, "give Zaalbar big stick".
Mission is a Scoundrel. She starts with high DEX, decent INT, and a slightly confusing mix of feats. What you do with her from there is up to you. Her biggest combat advantage is Sneak Attack, which continues to scale throughout the game, producing impressive damage output into the end game. This does mean, though, that she struggles with enemies who are immune to Sneak Attack.
You'll have Mission in your party some on Taris. Against most of the enemies you'll face there, she's adequate as either ranged or melee. But if you use her after Taris, you'll want to carefully specialize her for one or the other. Her companion quest involves combat, but she technically doesn't have to be present for it. So after the early game, you can pretty much use Mission as much or as little as you like.
Somebody on Reddit suggested this for Mission, which sounds fun:
If you want to cheese enemy bases? Oh, heck yeah. One of my favorite tricks is to stealth her in an enemy base (like the Taris one), have her sneak all over the base, repairing droids, picking up and re-planting mines, and then end at some terminal on the rear end. Slice in, cause an amazing amount of chaos, finish by overloading the terminal in the room she is in. It will knock her out but wipe all the mooks. And then, Player character just needs to mop up whatever Mission couldn't handle.
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Mission Builds:
Melee Mission
Ranged Mission