[RPG] How to cause a missed shapeshift roll for Dungeon World

Nothing in Dungeon World is a straight conversion of D&D – everything is re-imagined. Even the base classes provided can't be used to convert a D&D character straight across (for example, in stock DW there's no way you can make a Dwarven Druid, while you can easily do so in D&D 3.x without creating a house rules). A straight conversion of new material is never going to be simple. To convert new material, you have to re-imagine it fresh, with the aim of capturing the flavour and style of the material instead of the raw abilities.

For complex or powerful races, you are actually better off creating a new playbook for the race, with a few optional abilities to pick depending on what class they are. So instead of picking up the Fighter book and choosing a Fighter-class Drow racial ability, you pick up the Drow book and pick a Drow-race Fighter class ability. Doing it this way you get a very Dungeon World–style character: they're the one Drow (or Warforged, or Dragonmarked, or …) in the party, and their abilities have a flavour and mix that is unique to them.

You still have the challenge of balancing a new playbook, but you avoid the mess that can easily result from hacking up and rebalancing the existing class books.

No, you don't automatically lose the spell on a 6−. But you might.

It doesn't explicitly say whether you lose the spell, and that's on purpose. Missing on Cast a Spell gives the GM a chance to say something about what happens. That might include forgetting the spell or having it be revoked, but not necessarily. What happens next is what the GM says happens next, and that's all. If she doesn't say the spell is lost, then it isn't.

If you haven't got to the section on the rules for the GM, this will make more sense then. (If you're a player and your GM hasn't read the GM section yet, that's something your GM should do before running another session. Too many new Dungeon World GMs skip it because they assume it's just advice, but it's actually the rules for the GM player, and about 90% of the game!) The GM's rules are pretty explicit: you can do one thing, or another thing, but losing the spell and something else that's unrelated to losing the spell would take two GM moves, and she only gets one on a miss.

How player moves work is explicit too: do what the move says. Losing the spell is optional on a 7–9, and Cast a Spell doesn't tell you anything extra on a 6−, so it's not automatic in any way on the player's side of the rules. On a miss it's all up to the GM what happens, but the GM has rules to follow when deciding that.