Spawning Cacodemons in the sky instead on ground (Boom)

In addition: linedef type 242 will hide this spike for good (In Boom). Untexturing works well in vanilla.

Your solution is probably the best so long as it's as you said:

1) Outside the playable area or surrounded by something the player can't reach anyway

2) Doesn't interfere with the view of anything else

If you need/want to put the pole in a playable area, you can use a floor lower line at some point that Doomguy has to cross so that the pole is up when you first see the cacos but down by the time you could reach it. And you could use type 5 (plus a dummy sector) to do this instantly.

Here's a map to illustrate. At the start of the map, you wouldn't be able to get the BFG, but you cross a line that instantly lowers the invisible platform.

13 hours ago, RDETalus said:

I may have figured it out, I drew a 2x2 pixel spike with untextured sides and put a Cacodemon on top of it. So far it seems like it doesn't interfere with the player as long as it's kept outside of the playable area, and it doesn't seem to mess up the graphics of anything when it gets in-between the player and whatever is being looked at.

That method would work, but the untextured lines will lead to HOM. Given that the untextured lines are only 2 units wide, the HOM would be minimal and it might not even be that noticeable depending on how far away it was from the playable space. Of course, it is possible that with the right combination of monster and player movement, it could look strange and be evident that something was odd.

There are preferred ways to do this that would avoid the HOM effect, depending on the format.

Vanilla: Use self-referencing sectors (AKA crystal sectors). You could take that 2x2 sector (or any size) and make both sides of the linedefs reference the internal sector. Therefore, the sides of the 2x2 sector will not be rendered, but will still be there for collision purposes. Thus, the cacodemon will appear to floating in mid-air and you will be able to see through the sector (hence the "crystal" sector description).

Limit-removing: Same as vanilla

Boom: Use linedef type 242 to create a fake floor. The engine will treat the floor of the sector as being higher than what is visibly shown, and the cacodemon would appear to be floating in the air. Self-referencing sectors would also work, but the 242 effect is more stable and was specifically added to the Boom format to do the sort of things that you would use self-referencing sectors for in vanilla.

DiH/UDMF: I don't design with these, so someone else with more experience could correct me, but you can set the cacodemons to start at a particular height instead of starting at the floor.

Here's another method: give the cacodemons the MF_SPAWNCEILING flag in DEHACKED. That way, they'll be spawned right below the ceiling, just like hanging decoration.

You could even use some redundant item (such as the "dead lost soul" actor), make it a perfect copy of the cacodemon (same states, sounds, flags except for added SPAWNCEILING, hit points, etc.) and get this way a ceiling caco you can use in addition to normal floor cacos. However, note that they would be able to infight, since they would be technically two different classes of monsters, so you'd have to make sure to avoid mixing them in a given area.

I may have figured it out, I drew a 2x2 pixel spike with untextured sides and put a Cacodemon on top of it. So far it seems like it doesn't interfere with the player as long as it's kept outside of the playable area, and it doesn't seem to mess up the graphics of anything when it gets in-between the player and whatever is being looked at.

22 minutes ago, Pegleg said:

That method would work, but the untextured lines will lead to HOM.

There shouldn't be any HOMage unless viewed from above. This is the same thing that's done to make a basic bulletproof window and one of the ways to make a monster temporarily frozen.

Well, in Boom you could teleport it with silent teleport, but this is rather for advanced mappers.