To get the blue key on level 2, THE TERRAFORMER:

When you first find the blue key, it will be resting on a
short pedestal in the center of the room.  On the back of
the pedestal is a switch.  Activate it.  This will lower
the pedestal.  When you then attempt to grab the blue key,
it disappears.
The blue key will then pop in and out of existence along
the tops of the other pedestals in each of the four corners
of the room.  Eventually the key comes to rest on one of
them.  When this happens, 4 doors open up along the back of
the room, and behind each of these doors is a switch.  To
either side of 3 of these switches are a pair of short
vertical slabs rising out of the floor.  Find the one
switch where these slabs are missing.
When you activate this switch, the pedestal where the blue
key now rests will drop.  Run (remember your Run button) to
the pedestal before it rises again.
If the pedestal rises up before you grab the blue key, just
go back to the switch and try again.

If you activate any of the 3 switches that have those slabs
to either side, a section of the ceiling overhead will drop
down briefly and crush you, possibly killing you if your
health is low.

Hope this helps. :)                                                

--Led

www.ClassicDOOM.com
Support for console and PC Classic Doom games