At some point in your career as a DM you'll want to have a villain escape. Don't make his escape route shaped the way Skeletor's portal is shaped in this poster. You will regret it. Your players will remember forever and recount it at any opportunity. They will be scared by the purple and the innuendo inducing shape. I haven't had any horrid escape routes like this particular one. Early in my DMing career so long ago in the sundry past, I did have an enemy who had a minor teleport power that let him escape several dire situations. By the time the players finally cornered him they were incredibly ready to have his head. That wasn't the worst escape I had that campaign. The other big bad (the big bads were a trio of goblin brothers leading an army of goblins) was dragged to safety by his pet worg. The only consolation for the players was their preeminent execution of the one with teleport powers. All in all a bittersweet ending.
Let's hear about the ways, sanitary or otherwise, you've had your BBEGs escape.
Art is GIS for Skeletor
LooneyDM *escapes through a non-innuendo inducing portal*