Several of the danger rooms have gotten easier since the removal of constructs. I guess they made the changes with the last patch. Just thought I'd mention that.
Constructs removed from Danger Rooms
sorry, i don't know the names for danger rooms. the first room is square and divided into four section by spikes and has shock section in the middle of 3 of the sections. it used to be lumbers and wolvers and now it's slimes and gremilins, i think. it's much easier. the other one is that room with a wall of block and fireboxes around a square and spike plates in each of the four corners. it's still slimes with gun puppies spawning in waves 2 and 3, but there are no longer constructs chasing you around.
There are many different danger rooms and some have variations. Not all include construct.
Sometimes you'll find slimes, sometimes lumbers, etc. It adds more possibilities.
The first room i know, its not always lumbers and wolvers, its sometimes slimes and gremlins like you say, but then it usually has blocks in each square's corner. About the second room, i don't recall there being ever anything else other than slimes+gremlins+puppies on top and i've done it at least 6 times since they first introduced them. Ah, actually, the second danger room still exists. Its a little different tho, the construct version of that rooms has two walls of blocks, the first, is as you say, with blast blocks and the second is just blocks+ghost blocks, it still exists. Its the room with Scuttlesbots+Retrodes+Mechaknights+Gun Puppies.
i had shock lumbers and wolvers in that danger room recently(there were some puppy spawns too i think) and they gave me a hard time..in tier 1 D:!
btw i talkin bout the room with those spikes
http://media.spiralknights.com/wiki-images/1/13/Cross_Spikes_Danger_Room...
In some (but not all) arenas, they've exchanged mecha knights for gremlin thawackers and gremlin demos. It's a nice change of pace. But, it can be a bit hard in T3 where the healers can rez dead gremlins.
2 days ago i've done the room with Scuttlebots+Retrodes+Mechaknights+Gun puppies and a Gun puppies + Scuttlesbots room. What might you be talking about?