The authors write:
Fantastic Heroes & Witchery is a 430 pages rulebook, with all the information necessary to run a game of fantasy role-playing. Monsters and magical items are not provided (though they will come in later supplements), but you can use those from other editions of the game, so your books don’t become useless.
The rules are similar to those found in “the original game” and its simulacrums, but draw on several editions to create its own style. Fantastic Heroes & Witchery was done with the following goals in mind: ability to use most earlier material (monsters, magical items, modules, GM books, etc.) without conversion; simple and streamlined rules mostly based on the original game’s mechanics; but also new and different character classes, and many new spells. Overall, Fantastic Heroes & Witchery remains the same ancient game, but with slightly modernized rules plus a few options and additions.