Blood aids great sorcery.
Indeed we don't have a specific rule for Spellburn and we did so because of the philosophy we're following to use mechanics and technical terminology as little as possible.
In DCC, the Spellburn uses could be resumed (not strict) to the following:
- Sacrifice vital energy to a more powerful effect;
- Control a spell outcome;
- Use spells when you shouldn't;
As all characters can cast spells, we added those features to the Magic-User in their special abilities.
Blood Sacrifice: Covers item 1 and 3. Thou you can't use it more than once, as a MU gets more HP they will be able to do this more often without risk (they are the only Archetype that can break a spell's power limit of 5). The tax of sacrificing vital energy is represented here by the HP. Using this ability with a low HP value can cause critical damage to the spellcaster.
Dangerous Magic: Sort of covers item 2, you're still relying on the new outcome.
I could search for other examples to give. The thing is that we were trying to translate the DCC feel, not necessary an exact conversion into rules. E.g., I love spell duels, but it doesn't fit in this game's view. So for us, the Spellburn in the name is purely a homage.
Maybe Matt has something to say about it later, but I hope this helps.
Also, let us know if you try to run it with attribute sacrifice to add power to spellcasting. We might be missing on a big deal!
ps: This is also my current favorite ITO fantasy hack :P