Whirler Virtuoso

When Whirler Virtuoso enters the battlefield, you get {E}{E}{E} (three energy counters).
Pay {E}{E}{E}: Create a 1/1 colorless Thopter artifact creature token with flying.

Island

Attune with Aether

Search your library for a basic land card, reveal it, put it into your hand, then shuffle. You get {E}{E} (two energy counters).

Mountain

Confiscation Coup

Choose target artifact or creature. You get {E}{E}{E}{E} (four energy counters), then you may pay an amount of {E} equal to that permanent's mana value. If you do, gain control of it.

Forest

Harnessed Lightning

Choose target creature. You get {E}{E}{E} (three energy counters), then you may pay any amount of {E}. Harnessed Lightning deals that much damage to that creature.

Servant of the Conduit

When Servant of the Conduit enters the battlefield, you get {E}{E} (two energy counters).
{T}, Pay {E}: Add one mana of any color.

Aetherstream Leopard

Trample
When Aetherstream Leopard enters the battlefield, you get {E} (an energy counter).
Whenever Aetherstream Leopard attacks, you may pay {E}. If you do, it gets +2/+0 until end of turn.

Rogue Refiner

When Rogue Refiner enters the battlefield, draw a card and you get {E}{E} (two energy counters).

Evolving Wilds

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Aether Swooper

Flying
When Aether Swooper enters the battlefield, you get {E}{E} (two energy counters).
Whenever Aether Swooper attacks, you may pay {E}{E}. If you do, create a 1/1 colorless Servo artifact creature token.

Riparian Tiger

Trample
When Riparian Tiger enters the battlefield, you get {E}{E} (two energy counters).
Whenever Riparian Tiger attacks, you may pay {E}{E}. If you do, it gets +2/+2 until end of turn.

Empyreal Voyager

Flying, trample
Whenever Empyreal Voyager deals combat damage to a player, you get that many {E} (energy counters).

Longtusk Cub

Whenever Longtusk Cub deals combat damage to a player, you get {E}{E} (two energy counters).
Pay {E}{E}: Put a +1/+1 counter on Longtusk Cub.

Aether Meltdown

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature or Vehicle
When Aether Meltdown enters the battlefield, you get {E}{E} (two energy counters).
Enchanted creature gets -4/-0.

Consulate Turret

{T}: You get {E} (an energy counter).
{T}, Pay {E}{E}{E}: Consulate Turret deals 2 damage to target player or planeswalker.

Glassblower's Puzzleknot

When Glassblower's Puzzleknot enters the battlefield, scry 2, then you get {E}{E}. (You get two energy counters. To scry 2, look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)
{2}{U}, Sacrifice Glassblower's Puzzleknot: Scry 2, then you get {E}{E}.

Highspire Infusion

Target creature gets +3/+3 until end of turn. You get {E}{E} (two energy counters).

Bristling Hydra

When Bristling Hydra enters the battlefield, you get {E}{E}{E} (three energy counters).
Pay {E}{E}{E}: Put a +1/+1 counter on Bristling Hydra. It gains hexproof until end of turn.

Aether Theorist

When Aether Theorist enters the battlefield, you get {E}{E}{E} (three energy counters).
{T}, Pay {E}: Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Holdout Settlement

{T}: Add {C}. ({C} represents colorless mana.)
{T}, Tap an untapped creature you control: Add one mana of any color.

Maulfist Doorbuster

When Maulfist Doorbuster enters the battlefield, you get {E}{E} (two energy counters).
Whenever Maulfist Doorbuster attacks, you may pay {E}. If you do, target creature can't block this turn.

Voltaic Brawler

When Voltaic Brawler enters the battlefield, you get {E}{E} (two energy counters).
Whenever Voltaic Brawler attacks, you may pay {E}. If you do, it gets +1/+1 and gains trample until end of turn.