Flying

When Demon of Dark Schemes enters the battlefield, all other creatures get -2/-2 until end of turn.

Whenever another creature dies, you get {E} (an energy counter).

{2}{B}, Pay {E}{E}{E}{E}: Put target creature card from a graveyard onto the battlefield under your control tapped.

Whenever Gonti’s Aether Heart or another artifact enters the battlefield under your control, you get {E}{E} (two energy counters).

Pay {E}{E}{E}{E}{E}{E}{E}{E}, Exile Gonti’s Aether Heart: Take an extra turn after this one.

Whenever a permanent you control is put into a graveyard, you get {E} (an energy counter).

{T}, Pay {E}{E}{E}{E}{E}{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.

When Aether Hub enters the battlefield, you get {E} (an energy counter).

{T}: Add {C}.

{T}, Pay {E}: Add one mana of any color.

Whenever a creature enters the battlefield under your control, you get {E} (an energy counter).

{4}, {T}: Return target creature you control to its owner’s hand.

Flying

At the beginning of your upkeep, you get {E}{E}{E} (three energy counters).

Pay {E}{E}{E}{E}{E}{E}{E}{E}: Return all other creatures to their owners’ hands. Activate only as a sorcery.

Scry 2, then draw two cards. You get {E}{E} (two energy counters).

Double strike, haste

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

Whenever you get one or more {E} (energy counters), put a +1/+1 counter on target creature you control.

{4}, {T}: You get {E}.

Menace

Whenever Glint-Sleeve Siphoner enters the battlefield or attacks, you get {E} (an energy counter).

At the beginning of your upkeep, you may pay {E}{E}. If you do, you draw a card and you lose 1 life.

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.

{T}: Add {C}.

{1}, {T}: You get {E} (an energy counter).

{3}, {T}, Pay X {E}, Sacrifice HELIOS One: Destroy target nonland permanent with mana value X. Activate only as a sorcery.

Whenever an artifact or Artificer enters the battlefield under your control, you may pay {1}. If you do, you get {E}{E} (two energy counters).

Pay {E}{E}{E}{E}{E}{E}, Sacrifice Era of Innovation: Draw three cards.

Whenever you lose life for the first time each turn, you get {E}. (You get an energy counter. Damage causes loss of life.)

Pay {E}{E}, Sacrifice Gonti’s Machinations: Each opponent loses 3 life. You gain life equal to the life lost this way.

Whenever Rex, Cyber-Hound deals combat damage to a player, they mill two cards and you get {E}{E} (two energy counters).

Pay {E}{E}: Choose target creature card in a graveyard. Exile it with a brain counter on it. Activate only as a sorcery.

Rex has all activated abilities of all cards in exile with brain counters on them.

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

Vigilance, trample, haste

Whenever Liberty Prime, Recharged attacks or blocks, sacrifice it unless you pay {E}{E} (two energy counters).

{2}, {T}, Sacrifice an artifact: You get {E}{E} and draw a card.

Whenever one or more artifact creatures you control deal combat damage to a player, you get {E} (an energy counter).

Pay {E}{E}{E}: Create a tapped 3/3 colorless Robot artifact creature token.

Flying

When Aethersphere Harvester enters the battlefield, you get {E}{E} (two energy counters).

Pay {E}: Aethersphere Harvester gains lifelink until end of turn.

Crew 1 (Tap any number of creatures you control with total power 1 or more: This Vehicle becomes an artifact creature until end of turn.)

When Electrostatic Pummeler enters the battlefield, you get {E}{E}{E} (three energy counters).

Pay {E}{E}{E}: Electrostatic Pummeler gets +X/+X until end of turn, where X is its power.