Aether Herder is a common Creature — Elf Artificer Druid card from Aether Revolt (AER), collector number 102. Current market price: $0.15 (foil $0.05), TCGplayer market prices via Scryfall.
When this creature enters, you get {E}{E} (two energy counters). Whenever this creature attacks, you may pay {E}{E}. If you do, create a 1/1 colorless Servo artifact creature token.