I had an amusing thought I posted over on reddit and I figured I'd share it here too.
In Cold Days, we see further proof that Mab's idea of "training" is to just throw people into hideous situations, or maybe just make a few lazy attempts at murdering them. I think Harry can take this and run with it a little.
Dresden is the Warden of Demonreach, who doesn't seem to care what Dresden does with his captives. DR's response to questions is "YOU ARE THE WARDEN". So Dresden has carte blanche as to how he runs his operation.
Dresden could set up cage matches on Demonreach.
The Naagloshii were among the lowest tier of supernatural beasties. Last time Dresden went up against a Skinwalker without the island it beat him good, and even with the island he was only able to stand his ground for a little bit, and he was going all-out. Dresden's considerably stronger now, and far better at fighting without equipment.
The Naagloshii that are on the island are also undoubtedly weakened since they've been trickling energy out without replenishment. They'd be a good start.
Demonreach acting as a ref, Dresden could throw up the uber-circle and release a Skinwalker. It'd be great practice to fight something that even a Senior Council member would have a struggle against. If things got too tough he'd be able to have DR intervene. Sure the walker might get lucky, but this is Mab-style training so get-good. Once he can put them down without a problem, just start moving up the chain. That would have been a good way to spend a year trapped on the island.
I could even see him starting up a business doing this. Harry could set up some supernatural pay-per-view, start taking bets... I'm sure there's a bunch of supernatural beings, old gods of war, or other psychos out there that would love the chance to square off against some of the world's fiercest beings. The Erlking seems more of a hunter than gladiator, but in Changes he seemed to enjoy a good spectacle. Vadderung and his crew are all about the violence.
During his exploits throughout the year he could make an effort to collect bad guys instead of killing them and start up Harry's Colosseum; make 'em duke it out for reduced sentences.
Ha, it's just such a fun idea. People often bring up ways for Harry to get more powerful, but we always leave out the one thing that has always forced the biggest improvement: getting his butt kicked.
