So given that the Toxilargo only appears in one place in the game, in Briar Bone Barrage, and given that it's a T3-only level and a somewhat rare one at that, I thought I'd put together a playthrough video so people who haven't had the chance to play it can see what's what.
http://www.youtube.com/watch?v=AEzXOyAMY0E
For some reason I kept calling the level Dark City instead of Concrete Jungle. And I also forgot which gear I was wearing. /derp
All in all, I kinda feel a bit let down by the Toxilargo. I was expecting a standard enraged giant lichen colony with extra added poison clouds, but it was really a pretty dull monster to fight. Given the rather average difficulty I'm not sure A: why this level doesn't appear in T1 or T2, and B: why the toxilargo doesn't appear in poison themed lichenous lairs.
I guess it's a challenging monster if you don't have a gun? The mist seems to linger a bit, so it's probably tough (well, more like tedious) for pure swordies/bombers. I tend to kill lichen colonies with my Polaris, too. It's nice when you have them cornered and try as they might, their spikes can't reach you. I was expecting the Toxilargo to have spikes too, actually.