Amarsar, Hippogriff Rider

Griffin and Hippogriff creatures you control are
Mounts in addition to its other types and have
saddle 2. (Tap any number of other creatures you
control with total power 2 or more: That Mount
becomes saddled until end of turn. Saddle only as a
sorcery.)

Whenever a Mount you control attacks while
saddled, it gains horsemanship until end of turn.
(That creature can't be blocked except by creatures
with horsemanship.)