Gonti's Aether Heart

Whenever Gonti's Aether Heart or another artifact you control enters, you get {E}{E} (two energy counters).
Pay eight {E}, Exile Gonti's Aether Heart: Take an extra turn after this one.

Whirler Virtuoso

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

Aetherworks Marvel

Whenever a permanent you control is put into a graveyard, you get {E} (an energy counter).
{T}, Pay six {E}: Look at the top six cards of your library. You may cast a spell from among them without paying its mana cost. Put the rest on the bottom of your library in a random order.

Aetherstorm Roc

Flying
Whenever this creature or another creature you control enters, you get {E} (an energy counter).
Whenever this creature attacks, you may pay {E}{E}. If you do, put a +1/+1 counter on it and tap up to one target creature defending player controls.

Aether Refinery

If you would get one or more {E} (energy counters), you get twice that many {E} instead.
{T}: You get {E}, then you may pay one or more {E}. If you do, create an X/X black Aetherborn creature token, where X is the amount of {E} paid this way.

Decoction Module

Whenever a creature you control enters, you get {E} (an energy counter).
{4}, {T}: Return target creature you control to its owner's hand.

Sphinx of the Revelation

Flying, lifelink
Whenever you gain life, you get that many {E} (energy counters).
{W}{U}{U}, {T}, Pay X {E}: Draw X cards.

Amped Raptor

First strike
When this creature enters, you get {E}{E} (two energy counters). Then if you cast it from your hand, exile cards from the top of your library until you exile a nonland card. You may cast that card by paying an amount of {E} equal to its mana value rather than paying its mana cost.

Dr. Madison Li

Whenever you cast an artifact spell, you get {E} (an energy counter).
{T}, Pay {E}: Target creature gets +1/+0 and gains trample and haste until end of turn.
{T}, Pay {E}{E}{E}: Draw a card.
{T}, Pay {E}{E}{E}{E}{E}: Return target artifact card from your graveyard to the battlefield tapped.

Solemn Simulacrum

When this creature enters, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.
When this creature dies, you may draw a card.

Lightning Runner

Double strike, haste
Whenever this creature attacks, you get {E}{E} (two energy counters), then you may pay eight {E}. If you pay, untap all creatures you control, and after this phase, there is an additional combat phase.

Salvation Colossus

Flying, vigilance, trample
Whenever you attack, other creatures you control get +2/+2 and gain indestructible until end of turn.
Unearth—Pay eight {E}. (Pay eight energy counters: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Roil Cartographer

Landfall — Whenever a land you control enters, you get {E} (an energy counter).
{T}, Pay six {E}: Draw three cards.

Blaster Hulk

This spell costs {1} less to cast for each {E} (energy counter) you've paid or lost this turn.
Haste
Whenever this creature attacks, you get {E}{E}, then you may pay eight {E}. When you do, this creature deals 8 damage divided as you choose among up to eight targets.

Jolted Awake

Choose up to one target artifact or creature card in your graveyard. You get {E}{E} (two energy counters). Then you may pay an amount of {E} equal to that card's mana value. If you do, return it from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Sol Ring

Localized Destruction

You get {E} (an energy counter), then you may pay one or more {E}. If you do, each creature you control with power equal to the amount of {E} paid this way gains indestructible until end of turn.
Destroy all creatures.

Izzet Generatorium

If you would get one or more {E} (energy counters), you get that many plus one {E} instead.
{T}: Draw a card. Activate only if you've paid or lost four or more {E} this turn.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Razorfield Rhino

Metalcraft — This creature gets +2/+2 as long as you control three or more artifacts.

Guide of Souls

Whenever another creature you control enters, you gain 1 life and get {E} (an energy counter).
Whenever you attack, you may pay {E}{E}{E}. When you do, put two +1/+1 counters and a flying counter on target attacking creature. It becomes an Angel in addition to its other types.

Aurora Shifter

Whenever this creature deals combat damage to a player, you get that many {E}.
At the beginning of combat on your turn, you may pay {E}{E}. When you do, this creature becomes a copy of another target creature you control, except it has this ability and "Whenever this creature deals combat damage to a player, you get that many {E}."

Satya, Aetherflux Genius

Menace, haste
Whenever Satya attacks, create a tapped and attacking token that's a copy of up to one other target nontoken creature you control. You get {E}{E} (two energy counters). At the beginning of the next end step, sacrifice that token unless you pay an amount of {E} equal to its mana value.