Valorne, Honored Guardsman

Defender
Creatures with power equal to Valorne's power can't attack you or planeswalkers you control.
Whenever a creature enters the battlefield under
an opponents control, if there aren't any counters on Valorne, put a bravery counter on it. As long as Valorne has a bravery counter on it, it gets +X/+0, where X is that creature's power.