Mindspring Merfolk

Exhaust — {X}{U}{U}, {T}: Draw X cards. Put a +1/+1 counter on each Merfolk creature you control. (Activate each exhaust ability only once.)

Riverchurn Monument

{1}, {T}: Any number of target players each mill two cards. (Each of them puts the top two cards of their library into their graveyard.)
Exhaust — {2}{U}{U}, {T}: Any number of target players each mill cards equal to the number of cards in their graveyard. (Activate each exhaust ability only once.)

Draconautics Engineer

Exhaust — {R}: Other creatures you control gain haste until end of turn. Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)
Exhaust — {3}{R}: Create a 4/4 red Dinosaur Dragon creature token with flying.

Greenbelt Guardian

{G}: Target creature gains trample until end of turn.
Exhaust — {3}{G}: Put three +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Peema Trailblazer

Trample
Whenever this creature deals combat damage to a player, you get that many {E} (energy counters).
Exhaust — Pay six {E}: Put two +1/+1 counters on this creature. Then draw cards equal to the greatest power among creatures you control. (Activate each exhaust ability only once.)

Rocketeer Boostbuggy

Whenever this Vehicle attacks, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Exhaust — {3}: This Vehicle becomes an artifact creature. Put a +1/+1 counter on it. (Activate each exhaust ability only once.)
Crew 1

Sita Varma, Masked Racer

Exhaust — {X}{G}{G}{U}: Put X +1/+1 counters on Sita Varma. Then you may have the base power and toughness of each other creature you control become equal to Sita Varma's power until end of turn. (Activate each exhaust ability only once.)

Camera Launcher

Exhaust — {3}: Put a +1/+1 counter on this creature. Create a 1/1 colorless Thopter artifact creature token with flying. (Activate each exhaust ability only once.)

Spire Mechcycle

Haste
Exhaust — Tap another untapped Mount or Vehicle you control: This Vehicle becomes an artifact creature. Put a +1/+1 counter on it for each Mount and/or Vehicle you control other than this Vehicle. (Activate each exhaust ability only once.)
Crew 2

Rangers' Aetherhive

Vigilance
Whenever you activate an exhaust ability, create a 1/1 colorless Thopter artifact creature token with flying.
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.)

Hazard of the Dunes

Trample, reach
Exhaust — {6}{G}: Put three +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Boom Scholar

Exhaust abilities of other permanents you control cost {2} less to activate.
Exhaust — {4}{R}{G}: Creatures and Vehicles you control gain trample until end of turn. Put two +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Pit Automaton

Defender
{T}: Add {C}{C}. Spend this mana only to activate abilities.
{2}, {T}: When you next activate an exhaust ability that isn't a mana ability this turn, copy it. You may choose new targets for the copy.

Elvish Refueler

During your turn, as long as you haven't activated an exhaust ability this turn, you may activate exhaust abilities as though they haven't been activated.
Exhaust — {1}{G}: Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)

Skyserpent Seeker

Flying, deathtouch
Exhaust — {4}: Reveal cards from the top of your library until you reveal two land cards. Put those land cards onto the battlefield tapped and the rest on the bottom of your library in a random order. Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)

Loot, the Pathfinder

Double strike, vigilance, haste
Exhaust — {G}, {T}: Add three mana of any one color. (Activate each exhaust ability only once.)
Exhaust — {U}, {T}: Draw three cards.
Exhaust — {R}, {T}: Loot deals 3 damage to any target.

Agatha of the Vile Cauldron

Activated abilities of creatures you control cost {X} less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana.
{4}{R}{G}: Other creatures you control get +1/+1 and gain trample and haste until end of turn.

Rangers' Refueler

Whenever you activate an exhaust ability, draw a card.
Exhaust — {4}: This Vehicle becomes an artifact creature. Put a +1/+1 counter on it. (Activate each exhaust ability only once.)
Crew 2

Sabotage Strategist

Flying, vigilance
Whenever one or more creatures attack you, those creatures get -1/-0 until end of turn.
Exhaust — {5}{U}{U}: Put three +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Stampeding Scurryfoot

Exhaust — {3}{G}: Put a +1/+1 counter on this creature. Create a 3/3 green Elephant creature token. (Activate each exhaust ability only once.)

Prowcatcher Specialist

Haste
Exhaust — {3}{R}: Put two +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Skystreak Engineer

Flying
Exhaust — {4}{U}: Put two +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Redshift, Rocketeer Chief

Vigilance
{T}: Add X mana of any one color, where X is Redshift's power. Spend this mana only to activate abilities.
Exhaust — {10}{R}{G}: Put any number of permanent cards from your hand onto the battlefield. (Activate each exhaust ability only once.)

Afterburner Expert

Exhaust — {2}{G}{G}: Put two +1/+1 counters on this creature. (Activate each exhaust ability only once.)
Whenever you activate an exhaust ability, return this card from your graveyard to the battlefield.

Keen Buccaneer

Vigilance
Exhaust — {1}{U}: Draw a card, then discard a card. Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)

Boommobile

When this Vehicle enters, add four mana of any one color. Spend this mana only to activate abilities.
Exhaust — {X}{2}{R}: This Vehicle deals X damage to any target. Put a +1/+1 counter on this Vehicle. (Activate each exhaust ability only once.)
Crew 2

Pacesetter Paragon

Exhaust — {2}{R}: Put a +1/+1 counter on this creature. It gains double strike until end of turn. (Activate each exhaust ability only once.)

Greasewrench Goblin

Exhaust — {2}{R}: Discard up to two cards, then draw that many cards. Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)

Adrenaline Jockey

Whenever a player casts a spell, if it's not their turn, this creature deals 4 damage to them.
Whenever you activate an exhaust ability, put a +1/+1 counter on this creature.