Duel of Champions

Changes the Battlefield to "Duel of Champions".
At the beginning of each round, you may select
one of your Warriors; if you do, your opponent
must also select one of their Creatures. Only
these Creatures can attack, until one of them is
killed. Negate all other Creature abilities on the
field. No non-Creature cards can be activated
from the hand until this effect is over. Creatures
on the side of the field of the winning Creature
gain 10 Speed and 20% Max HP for the duration
of the roun