Encounter combining baddies and traps

[Grizzled Gryphon]

Is this done? I have an idea where the party enters the area, and sees the baddies within charging range. So, the run up and beat em up type does his thang, only to discover the floor isn't quite as solid as it seems. Either a trap door or illusion over a pit.

Is this unfair? After all, the skill monkey hardly had a chance to find the trap. Do I count the traps CR in with the baddies? Hardly seems worth it, though, as the pit trap is pretty low on the CR of traps.

My idea is two bone creature fighter types guarding the far door. In the pit would be a Shadesteel Golem, and a couple of Shadows. Not sure how I should rate the CR of this encounter, though. I will go with the illusion covered pit. Pit goes all the way across the floor which is 30 ft., and the pit is 20 ft. deep.

[Grizzled Gryphon]

No comments? Bummer.

[madtinker]

Sounds like a fun encounter.

If this were my encounter, I would use the effective encounter level for multiple monsters (Table 3-1 in DMG). Using the challenge rating for the trap seems appropriate, but you may have to adjust the encounter level from that if you stack the odds too heavily against the PCs.

[Glimbur]

This is a good idea, but the CR is a little hard to manage. Start with the base difficulty of all the monsters, and then throw in a +2 or so depending on how stacked the battlefield is. Maybe.

[Humble Master]

Putting traps in the room with some enemies is a good and perfectly fine idea. The PC's shouldn't just look for traps in the corridors and at every door. As for the CR and thus XP reward I would probably just eyeball it. Maybe +2 or +1 CR depending on how bad the trap is.
Based on your description, the pit seems like it would only be a minor inconvenience compared to the Shadesteel golems and Shadows which are better measured as creatures than parts of a trap.

[GutterFace]

Illusory Pit is amazing. i had fantastic luck with this and Illusory Feast.

it really makes people thing outside the box to finish encounters. the pit its self is devastating to martial classes with mid to low will saves. especially if you have it covered and then revealed

if you are throwing in baddies with the trap, i would say possibly vertigo field would be better with a mini boss. really make those players suffer.

i had a stained glass golem, in a room with a proximity vertigo field trap. it was a 'chapel' type room with the trap centered on an alter with a beautiful stained glass window (lol) above it.

illusory feast trap in a mess hall with hidden enemies also can be fun.

but to your question yes you should add the cr of the trap to the fight depending on how your party is tiered. it if's say a magical trap. if its like a mundane arrow trap i would say no since the party should be able to avoid that with ease

[Brookshw]

It's legit, there are several similar encounter set ups in classic modules. Have fun!