As I understand it, you could say "For use with 5th Edition Dungeons & Dragons," and you'd still be in the clear as long as you stayed away from D&D trade dress. That's called "nominative use," and it's one of the cases where you can use somebody else's trademark. It's what KenzerCo did with "Kingdoms of Kalamar."Additionally "5th Edition" is not the official title of the new edition, the title is "Dungeons and Dragons" and 5th edition is simply a reference point when clarity is necessary, thus "5th edition compatible" is not a protected term.
But, again, CONSULT A LAWYER before relying on this.
