Terrifying Conflict

Choose target opponent. You and that opponent
both search your libraries for a creature, reveal it,
and put it onto the battlefield. They then fight.
You and the chosen opponent shuffle your
library afterwards.
"Those Pokemon fighting... Groudon and Kyogre...
The two super-ancient Pokemon were awakened from
a long sleep. And now they are smashing each other
with their uncontrollable energy..." - Steven Stone