1) Personally I love the way Theo looks in panel 3, and we'll ignore how I forgot to completely colour his pants in.
2) The sucky thing about doing back-story ones (This'll be mostly third-and-fourth-year) is that Tom Felton had that Spike-Geled-back look that sucks to draw. Just a side-note, Theo has red hair in this strip, canon (not yet established) be damned.
3) The walls change on purpose 'cause it doesn't want to be a dungeon every thirty seconds. Sometimes it wants to be disco-polka-dotted, and sometimes it wants vinyl siding.
4) ...The house elf in the corner looks rabid.