Julian, did you design it, I mean the concept and layout?
Very fascinating! I'm ashamed to think I never imagined this idea for a t-shirt.
I'm a super fan, I will very likely purchase that one or print my own variation (one that would somehow visualize Commodore/Amiga computer logo, with every other new playable platform logo, for example, although I realize there are probably legal complications with mass public marketing of my design, since Amiga technically still in business & Windows, Linux might object), not likely an issue for your design, can't imagine Kalle objecting.
Being cheeky, not meaning to be critical in any way, for my back side screenshot, I would like about 6 players shown swarming around same room, battling one of each monster, with a book sitting on a pentagram, and the same color Knight as front logo, taking a swing at the book with a wand (thus being the Winner). LOL... Asking too much? Just trying to be funny and add my creative 2 cents to your already excellent brilliance

Good to see Stephen endorses usage of his website branding = publicity = awesome!
If I choose to buy the cafepress shirt you displayed, I am curious, what does the fine print on the back of shirt say? I can't read it from image.
Thank you for presenting this, I truly love it, and sharing it now with everyone I know that plays, or used to play, or might be interested.