Talk:Outsider's Mark/@comment-80.7.97.231-20141230122913/@comment-5607198-20141230192501

It's both, like almost all games that use Mana.

Mana is a gameplay representation (and balancing mechanic) of the idea that magic requires the use  of one's mental will (Fable actually skipped a step and just REFERRED to mana as Will).

Magic doesn't require physical energy, but it is MENTALLY taxing. Think about how exhausted you feel after a very tough exam. You didn't do anything to tire yourself out, but you worked so hard recalling knowledge and thinking of solutions, your brain tells you that you've exerted yourself so it has a chance to reset.

Piero's anti-plague goo has a side effect of heightened alertness and mental stress relief. That way, you can continue thinking (and casting) without becoming unfocused or confused.