Best Small-format Build: Balzar's Blunder by Mary Ann

Here’s their story:

Balzar, an apprentice mage, regretted sneaking into the Clan Rattail cavern on his own.  In desperation, he cast Permanent Magnificent Mansion off a stolen scroll in what he thought was a defensible position.  And he’s been stuck there ever since.  117 days and counting, surrounded by goblins and their trained giant rats.  To pass the time, he occasionally takes potshots at one or two with a magic missile.