It's quite easy actually:
To play ELO you must be level 20 (6 levels to go )
Then you must have a valid deck for elo, meaning you must have a deck that if you add up the yellow stars on the
card (current level of your character), you get to 25 or less and also without doubles, and certains characters
(general, dj korr and kiki, as of now). The whole idea is to make a deck strong enough to crush your enemy (wich is
much more difficult with this limitation )
You don't have to put anything next to your nickname because as soon as you fit the above requirement, you'll
show up with a little "pillz" in the game room, and your current elo level).
ELO is real fun and great way to use strategy when you want to take a break from levelling your cards.
And sure.. there are the prizes, nice collectors cards and rare cards (more on that in "Staff announcement".