Hi Xenio - quick question - at the end of an adventure, during the Advancement phase - can a player increase his or her Control die instead of a skill?
It depends on the scope of your game, since it makes characters a bit more durable.
If you're running a longer game that'll last many sessions, I would definitely allow it. Now if it is a shorter game, I don't recommend it, the smaller Control die keeps a sense of urgency and danger.