That's fantastic! But I don't think I could resist the temptation if I were the DM to eventually menace the group with a bunch of Mind Flayer tax collectors from the Inter-dimensional Revenue Service.
Or maybe they'd be immigration agents. "Papers, please!"
Make that "Cerebellums, please!"
Precisely what I was thinking (well, not necessarily with Mind Flayers). Someone institutes a tax pegged to the value of the lodging or the food consumed. Or per spell level used to establish a temporary shelter on interdimensional property (that belongs to some god, or warlock patron, after all). Because why exactly do these adventurers feel like they can pop in, kill OUR monsters, and not contribute anything to the education of our people or the quality of our roads to the dungeon?
I asked the party Rogue about this. After some Evasion, he said that since tax collectors can't get in through the portal, as long as we don't go out, they can't touch us.
However, the Wizard consulted his library and thought that the mind flayers' ability to plane shift might allow them to break in. But he wasn't sure if the extra
N-dimensional space we were in, constituted a plane as such that they could shift to, or if we were still technically in the prime material plane, just wrapped up inside a vibrating 11-dimensional brane the length of a plank.
That didn't help, because we hadn't a clue what he was talking about, so we got the party Cleric to try to
Plane Shift himself out of the MMM and into the teleport circle in his home temple, reckoning if he could get out, they could get in. Unfortunately, he disappeared and never came back. We were a bit worried about him, actually. We tried a
Sending but there was no answer.
So we asked the DM how much he wanted in taxes, and please could we have our Cleric back? He rolled some dice, gave an evil chuckle and said the taxes were paid
for the time being but we'd have to pay the temple to do a Resurrection on the Cleric if we wanted him back, on account of him needing a new brain.
So now we needed a 1000gp diamond. The Barbarian solved this by picking the Halfling Rogue up by his heels and shaking him and guess what fell out?
We're good.