Assault griffins are griffins that have been domesticated and bred for war.
"The Simic offer a prize to any biomancer who can breed a krasis to match a griffin in the air. It's never been claimed." -Libuse, Boros sergeant
"Fine soldiers guarded the northern front. They waited for two-legged foes and left the skies unheeded." -General Avitora
"Griffins do not serve. They give freely to those they trust." -Amira, skycaptain of Thune