Stormtreader Ghoul

Flying, instability (At the beginning of your upkeep, you may pay {X}. If you do, this creature has base power and toughness X/X, and it can't have -1/-1 counters placed on it.)
Stormtreader Ghoul can't be blocked by creatures with a lower power.
"At the sight of the ghost of the sea, most would flee. To be honest though... so would I"
-Atmos, High Captin