It's Not Much, But It's Honest Work

You get this achievement in the mini-instance called 'Awakening The Machine' which you can access by talking to [npc=217128] in Gundargaz in The Ringing Deeps. Twenty waves of mobs come at you - keep the Keeper alive and out of trouble and the 20th wave is the [npc=229782]. Kill it before it kills you or the Keeper and you get this achievement.

The waves of mobs do not seem too bad - as a healer, it was no problem doing this. Pick up Gearing Up for Trouble from [npc=216164] first.

Found this pretty easy as a 567 mage. Could easily have done it lower. Some notes:

I didn't see a time-limit on the "break" you can take every five waves. I sat down waiting for my lesser cooldowns to come back at wave 15 and wasn't forced into the next one until I talked to him.

When medbots die, they drop some green stuff on the ground that will heal you and also the guy you are protecting. The heal size varied massively for me, ranging from anywhere between 5% of his health to almost a third. Drops often enough that you shouldn't need to worry about getting attritioned down while you are gathering aggro across 20 waves. Started spawning at wave 11 for me. These health puddles DO NOT last forever, you can save them a bit into the next wave but you can't stockpile them as long as you like and they will disappear if unused. It was pretty unclear what the medbots do when they are alive, I would guess that they were trying to heal something - but I usually found them AFK-casting something halfway across the room after I killed everything else. I assume I accidentally did the correct move of dragging the other mobs away from them, but these can easily be ignored until the end of the wave.

Nullbots target a mob and make them immune to damage. I just nuked them directly, so this doesn't do much as they don't do it right from the first second.

The caster dwarves die when you interrupt their spell. Counterspell insta-kills one, I usually just killed the other directly as my top priority after the pylons.

Nuke the pylons down, they do quite a lot of damage and will ignore you to DPS the guy. Top priority for me.

Poke swarmbots once to aggro them and get them to follow you. I didn't spend much time in melee versus the exploding bots and the shredder, but even the crowd at level 19 wasn't overwhelming in terms of damage - one of those mobs places 4 lava orbs around you that will fire off in a cross pattern away from your character. These orbs don't rotate as you do, so just try not to point it directly at the guy you are protecting and it should be fine. The lava doesn't linger for long even if you screw it up.

The boss at level 20 evaporated in approximately five seconds after I blew every cooldown. The wave at 19 was significantly more challenging, but still not that difficult - the wave seemed primarily focused on killing me as a means of providing challenge rather than killing the target, and I was never forced to use the majority of my defensives aside from basic kiting and Ice Barrier.

Simple guide that should get you this achievement with no problems:

#1 Go to The Ringing Deeps & pick up quest from [npc=216164] then speak with [npc=217128] to que for the scenario.
This doesn't get even remotely challenging until wave 15-20. In the future with more gear even that will be a joke.

#2 Aggro and kill everything you see.

#3 The mobs that are channeling abilities (That can be kicked) will die immediately once you interrupt them in any way (Includes knockbacks, stuns, silences, whatever)

#4 Green vials will drop on the floor, run on top of those to heal both yourself and the NPC you'll be protecting. (The vials despawn after a while)

#5 Last boss is nothing special and was easier than the last few waves. Just an elite mob with about 6000k HP.

Gratz!