Elven Cavalry Charge

At the beginning of your upkeep, amass Elves 1.
(Put a +1/+1 counter on an Army you control. It is
also an Elf. If you don't control an Army, create
a 0/0 black Elf Army creature token first.)

At the beginning of your end step, untap up to X
basic lands, where X equals the power of target
Army creature token you control.