Shadowverse

But I'm not afraid of the tournament because I might lose; the time zone difference prevents me from participating.

Considering that (all/most) players are active on the forum at night, this might not be a problem.

I don't want to deal with Steam.

It only takes two minutes to register and install. Overall, I think choosing a league format for the tournament would be a good idea. This way, we can set a longer timeframe (i.e., play when there's time, rather than having to adjust to specific rounds), and it will provide more experience.