Speaking of Malta. Remember the Titans?
Two of the smaller Hercules Titans were capable of combining to form a Zeus. I was never certain of what triggered it - obviously it was due to a certain level of damage, but precisely where that trigger was... it seemed to vary based on circumstances. (Plus it might've been tweaked by the Devs over time.)
Still - I recall that - like the Warwolves, I'd never seen it HAPPEN or even heard about it until I was on a solo mission. I'd dealt with enough Malta by that point that I knew - despite appearance to the contrary - the biggest threat in any group is NOT the giant robots, it's that GODDAMN SAPPER.
This is a pretty sharp memory - I was in one of the tech labs in one of the large rooms. And there's a group there with 2 Hercules, a Sapper, and a couple of those guys who drop turrets. So I drop the sapper with an Eagle's Claw kick and a couple of stacked red inspirations, then take out the two turrets and their handlers, all while the Titans are blanketing everything with corkscrewing missile trails and blue energy beams. I was on my MA/INV scrapper (Same one as in that previous story with the 5th Column early in this thread) and this was before the INV nerf for scrappers, so she was pretty darn tough enough to weather the damage from the Titans until she could get to them.
And I start bashing on the first one pretty hard. The other is standing about 3-5 meters away. I think it was down to about 1/4 health, and it turns away from me and - I thought it was going to be a "runner" - but no -
He turns only to run directly at the other Herc. And then the first Herc JUMPS and... FOLDS... in mid-air around the other Herc, until they form the Zeus. (A boss at full health of course).
You know... You can tell when you are obviously a truly hard-core geek when you get taken out because you're too busy gawking at something and having a "nerd-gasm"...
"Oh my GOD THAT IS SO COOL!! Look at the way that folded! I never knew! It makes so much SENSE!
One torso stacked on the other and it's PERFECT. I can see exactly where the arms fold up around the chest!
And there's the feet! So that's why a Zeus has those up there!
...and... and...
...and damn. I'm dead...
...
... Screw it. It was worth it." 
Of course, if you've never had any warning ahead of time, encountering the KRONOS Titan for the first time isn't just a surprise, it's a full-on OH CRAP IT'S GODZILLA moment... God help you if you were solo-ing that run...
Fortunately, I didn't have THAT happen to me. But even so - even knowing it was coming. Even having been warned... To see that thing stomping over the hills toward you in Founders Falls for the first time...
...
"mommy!..." 