Cheapest priced copy (The Lost Caverns of Ixalan Commander): $0.69 at Card Kingdom, near mint, their price list as of .
Patron of the Vein 
Creature — Vampire Shaman · 4/4 · Rare · Commander 2017 · #20
Flying
When this creature enters, destroy target creature an opponent controls.
Whenever a creature an opponent controls dies, exile it and put a +1/+1 counter on each Vampire you control.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.69 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2017 | 20 | Rare | $0.99 | — |
| The Lost Caverns of Ixalan Commander | 207 | Rare | $0.69 | — |
| Crimson Vow Commander | 135 | Rare | $0.69 | — |
3 rulings from Wizards of the Coast
- 25 August 2017If 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.
- 25 August 2017Destroying 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.
- 25 August 2017Patron 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).