Vigilance
Whenever an opponent attacks with three or more creatures, you may have Eternal Sentinel become an artifact creature until end of turn.
Spellcharge 3

Target creature gains hexproof until end of turn. Teach it vigilance.

Enchant creature with another Aura attached to it
Enchanted creature gets +3/+3 and has trample, vigilance, and reach.

When Everpresent Rot enters, create a 1/1 green Saproling creature token, surveil 1, then you gain 1 life.
When one or more permanent cards leave your graveyard, return Everpresent Rot to its owner's hand.

Deathtouch
Other Gorgons, Snakes, and Basilisks you control get +1/+1.
Whenever a creature with deathtouch you control deals combat damage to a player or planeswalker, create a Treasure token.

Executive Office enters tapped.
{T}: Add {B} or {R}.
{4}: Make a pledge. Activate only as a sorcery.

When Exemplar of Grit dies while attacking, return it to the battlefield tapped under its owner's control with a defender counter on it.
When Exemplar of Grit dies while blocking, return it to the battlefield tapped under its owner's control with a decayed counter on it.

{3}{R}: Exile the top card of your library. You may play that card until the end of your next turn.
{7}{R}: Exotic Transformer deals damage equal to its power to any target.

Target creature gains haste until end of turn.
Draw a card.

Trample, haste
Decayed

Decayed
{1}{B}, Exile Expendable Medic from your graveyard: Return target creature card from your graveyard to your hand. Activate only as a sorcery.

Decayed
{2}{U}, Exile Expendable Researcher from your graveyard: Return target instant or sorcery card from your graveyard to your hand. Activate only as a sorcery.

Draw three cards.
Surface {5}{U}{U}

Explosive Redemption deals 4 damage to target creature. When that creature dies this turn, return it to the battlefield under your control. It gains haste. Sacrifice it at end of turn.

You may cast this spell as though it had flash as long as {U} is spent to cast it.
Return target creature card with mana value X or less from your graveyard to the battlefield tapped. If {R} was spent to cast this spell, create a token that's a copy of that creature. It gains haste until end of turn. Sacrifice the token at end of combat.

Flash
Vigilance
Whenever Exuberant Caprisaur attacks or blocks, you gain 2 life. Then if your life total is greater than 20, put two +1/+1 counters on Exuberant Caprisaur.

Reveal the top four cards of your library. Put up to two permanent cards from among them into your hand and the rest into your graveyard. You may put land cards onto the battlefield tapped rather than your hand.
Flashback—{3}{G}, Tap an untapped Ruin you control.

Flying
Whenever a creature you control with flying deals combat damage to a player, you may pay {U/B}. If you paid {U}, draw a card. If you paid {B}, that player discards a card.

Flying, vigilance
If you would draw a card, you may exile a card from your graveyard instead. When you do, reveal cards from the top of your library until you reveal a card that shares a card type with the exiled card. Put that card into your hand, and the rest on the bottom in a random order.

Enchant creature
When Fable of Tooth and Fur enters, create three 2/2 green Wolf creature tokens.
Enchanted creature gets +1/+1 for each creature you control and gains trample.

Ward {2}
Spells and abilities you control that target Fabulous Serpent cost {2} less.
{2}{U}: Creatures you control get +1/+1 until end of turn.

Exile the top two cards of your library. You may play those cards until you next cast a spell from your hand.
Flashback {3}{R}{R}

Target creature gets -3/-2 until end of turn.

Choose one —
• Target player sacrifices a creature with the least power among creatures they control.
• Target player sacrifices a creature with the least toughness among creatures they control.

Enchant creature you control
When Fall from Nyx enters, destroy target artifact or land.
Enchanted creature gets +2/+0.