Originally Posted by thejinks
ya know honestly i have this horrible sinking feeling is alot of them might be by doing the stage battles on multiplayer. as i dont have online ill be ragin if they are. when i finished i had only 1 concept art for the tainted coil and 1 for the drowning doom. started then fiddling around on the ai practice stage battles for those random acheivements and unlocked some that way. apart from that i think it could be by hoppin on them an killing a few enemies. dunno.
Your on the right track. Create a custom game on the feeding pit and don't invite anyone in (I think you can do this offline to). Capture all the Fan/booth points but be careful not to let you troops attack the enemy stage (it an a booth will be present just destroy the booth).
Next create a Waypoint/flag in the feeding area and start spawning units. The monster will kill off your units so you won't hit the capping limit. Keep spawning a unit till you get a "concept art unlocked" then move onto the next unit. The Tainted coil took the longest with spawning/reproducing wth the right units.
To get the concept art for the actual "Stages/Fortresses" upgrade them fully then Double team with the stage (so your on the Mic). Leave your character there for OVER 5 mins. when you jump off you'll get the concept art for that too.
NOTE: If your getting the animal concept art too make sure you kill them in hand-to-hand or with guitar attacks. Kills with the The Duce don't count.