A/D - Left/Right.
W - Shoot Orb.
S - Cast Spell from Card.
Left/Right Arrow keys - Left/Right.
Up Arrow keys - Shoot Orb.
Down Arrow keys - Cast Spell from Card.
Destroy orbs by making matches of 4 or more. Catch any falling cards. For every card you catch, you can cast a spell on the other player (by pressing S). When your mana tops up, you will automatically cast a spell on the other player.
If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).