Heraldo de Garruk

Hexproof from black means that Garruk's Harbinger can't be the target of black spells your opponents control or abilities your opponents control of black sources.

If Garruk's Harbinger deals damage to a planeswalker greater than their loyalty or to a player greater than their life total, you look at a number of cards equal to that full amount of damage dealt, not just that loyalty or life total.