Rangers are Next Level Dumb, and you need to hold their hands to the max
to start off go into settings and turn on assist mode
make sure to turn Immortality on, this only works on you. now also make sure to set Damage Reduction and Ammo Recovery to 100
heres is the intercom where you call the rangers
you need to call them before you enter combat or the game wont let you.
enemies wont always spawn and you may need to travel 3 or 4 times to get them to show up
ive found the best two places to travel between are the AWE loading bay and the Collapsed Department. both can be used to unlock this achievement.
just walk into the next rooms over where enemies spawn after hitting the call ranger button to see if you got lucky, if not travel back and forth until they do.
now to actually doing it.
Equip both Grip and Spin.
you need to do about 98% of the damage to each enemy and just hope the ranger lands a shot
just use the guns, because everything else has a risk of killing some of the group.
get everything as low as you can without killing and stand in the rangers line of sight. well tanking all the damage
if the ranger isnt attacking at all, you can smash up what they are hiding behind. they will move to another form of cover.
enemies tend to attack faster then the ranger can and stop them from ever attacking, so you may need to shot things, pull aggro away from them. just hope you didnt kill it
if an ORB spawned, you can get it low and use Seize to take control of it. it will now heal you and most importantly the ranger.