Reach
When this creature enters, destroy all creatures with flying. Put a +1/+1 counter on this creature for each creature destroyed this way.
A creature with indestructible or a creature that regenerates won't count as having been "destroyed this way."
If a creature with flying would be destroyed, but an Aura with the umbra armor ability is destroyed instead, Whiptongue Hydra won't count that creature or that Aura as a "creature destroyed this way."