I've found that many achievement guides fail to detail how best to get this achievement, so I figured I'd do it myself.
Untouchable Achievement Walkthrough
For this achievement, I chose the Aegis Mech, the Siege Mech, and the Swap Mech, with Mafan as a pilot. They're all powerful in their own right, but in this team they each fulfil different roles.
- The Aegis Mech has one of the game's strongest counters, as swapping an attack's direction is usually more effective than pushing. Furthermore, avoiding pushing also avoids slamming vek against your own mechs, which would beat the whole point of this run. Use it to clean up the problematic vek that the other two can't deal with.
- The Siege Mech is probably in the top 5 best mechs of the entire game, but that's tangential. Use its excellent push-damage skills to clear out large groups of small health foes (particularly useful against spiderlings and robots) or to clear out the vek that decide to surround the Aegis. Used right, you should be getting triple kills on a regular basis with this. I picked this mech because it is most effective at a distance and therefore out of harm's way.
- The Swap Mech is also excellent. In this team, it functions as your utility class, shuffling enemies to where they can kill each other. Not much to say here.
- Mafan is your pilot of choice because he can avoid any and all damage. If you haven't unlocked him yet, check out this guide on how to do so. If you haven't unlocked him and won't, Bethany Jones is a serviceable alternative. You want to place him in the Aegis Mech, upgrading your move skill.
Picking your island
Using the Threat Scanner, avoid any island with the Blast Psion. It'll give you too many headaches not to mention too much damage.
For the same reasons, avoid islands with vek that deal area-of-effect damage. Best stick to simple, one-target enemies. Remember that this team, despite being strong, only needs one hit to go down.
Pretty awful combo of enemies.
The lower image is a far better matchup for you.
As soon as you get a power core, switch Mafan to the Swap Mech, and power the "Gain Shield" upgrade with your new pilot. Doing this means two of your three pilots will have constant regenerating shields.
In order, your upgrade priorities are:
- Gain Shield -Aegis.
- +2 range - Swap.
- Buildings Immune - Siege (You won't get this far, though.
Choose your battles
- Avoid "Block vek from spawning X times" missions. This is a recipe for disaster.
- Be careful with defense missions, but only because they're generally annoying.
- Choose "Take no more than X damage" missions. You're already doing that, so keep at it.
Kill missions are perfectly fine, your team is great at getting kills.
Deploying your mechs
Place your Swap and Aegis Mechs front and center; that's what they're good for.
Pick missions that offer what I like to call a "shooting range" for your Siege Mech: a row/column far away from the action where it can shoot without being in the thick of it. The image below is an example of a level that's going to be painful for your Siege Mech. It won't have a vek-free shooting space.
The image below shows a level that is significantly better.
Fighting the good fight
That's about all there is to say. You can afford the grid damage early on, so when it comes to failing the objective and letting a couple hundred innocents die, you know what to choose.