NO FUN ALLOWED 5e

Rope trick lasts 8 hours at 8th level. Plus monsters that can see invisible will ambush the hell out of you.

8 hours is enough for a long rest, and therefore another rope trick with net neutral spell slots.
I will admit to probably incorrectly remembering it lasted longer than that at lower levels though, I'll double check later when I have my book.
Also the DM wrecking their setting to include shit-tons of invisible monsters counts as a win in my book.

>t. Cuckolds who let themselves get fucked over, then skulk off and hide and pretend they are "taking the high road" to rationalize their pussified actions.
I would say: play a rogue. Get into battle with some enemies when one of his snowflake DMPCs is along. Try to draw the monsters to you and him with Persuasion or Intimidate checks to goad them, but if you can't, it doesn't matter. Wait until the DMPC is at low health, then sneak attack him. If he is in melee with another creature, it counts for sneak attack.

You may as well be announcing your thread is bait. Everyone laugh at OP.

Portals only have one surface, don't they? Just make the portal face a wall, such that the creature would have to be smushed up against the surface of the wall and look upwards just to see the portal's 'open' side.