8/25/2017 Destroying a creature with Patron of the Vein¡¯s first ability causes its last ability to trigger if Patron of the Vein is still on the battlefield.

8/25/2017 Patron of the Vein¡¯s last ability puts a +1/+1 counter on each Vampire you control, including itself, even if the creature that died can¡¯t be exiled (most likely because it was a token).

8/25/2017 If Patron of the Vein and a creature an opponent controls die simultaneously (perhaps because they fought or were in combat together), Patron of the Vein¡¯s last ability triggers, but Patron of the Vein won¡¯t be on the battlefield as that ability resolves. It can¡¯t be saved by the +1/+1 counter that would have been put on it. The same is true of any other Vampires you control that die at the same time. Your remaining Vampires will each get a +1/+1 counter.