Akroan Skyguard

Flying
Heroic — Whenever you cast a spell that targets Akroan Skyguard, put a +1/+1 counter on Akroan Skyguard.

Elite Skirmisher

Heroic — Whenever you cast a spell that targets Elite Skirmisher, you may tap target creature.

Wingsteed Rider

Flying
Heroic — Whenever you cast a spell that targets Wingsteed Rider, put a +1/+1 counter on Wingsteed Rider.

Boon of Safety

Put a shield counter on target creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Scry 1.

Hyena Umbra

Enchant creature
Enchanted creature gets +1/+1 and has first strike.
Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)

Veil of Secrecy

Target creature gains shroud until end of turn and can't be blocked this turn. (A creature with shroud can't be the target of spells or abilities.)
Splice onto Arcane—Return a blue creature you control to its owner's hand. (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Mortal's Ardor

Target creature gets +1/+1 and gains lifelink until end of turn. (Damage dealt by the creature also causes its controller to gain that much life.)

Tethmos High Priest

Heroic — Whenever you cast a spell that targets Tethmos High Priest, return target creature card with mana value 2 or less from your graveyard to the battlefield.

Moment of Triumph

Target creature gets +2/+2 until end of turn. You gain 2 life.

Infiltrate

Target creature can't be blocked this turn.

Arrester's Zeal

Target creature gets +2/+2 until end of turn.
Addendum — If you cast this spell during your main phase, that creature gains flying until end of turn.

War-Wing Siren

Flying
Heroic — Whenever you cast a spell that targets War-Wing Siren, put a +1/+1 counter on War-Wing Siren.

Enter the Enigma

Target creature can't be blocked this turn.
Draw a card.

You Come to a River

Choose one —
• Fight the Current — Return target nonland permanent to its owner's hand.
• Find a Crossing — Target creature gets +1/+0 until end of turn and can't be blocked this turn.

Wavecrash Triton

Heroic — Whenever you cast a spell that targets Wavecrash Triton, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Shadow Rift

Target creature gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)
Draw a card.

Lagonna-Band Trailblazer

Heroic — Whenever you cast a spell that targets Lagonna-Band Trailblazer, put a +1/+1 counter on Lagonna-Band Trailblazer.

Karametra's Blessing

Target creature gets +2/+2 until end of turn. If it's an enchanted creature or enchantment creature, it also gains hexproof and indestructible until end of turn. (It can't be the target of spells or abilities your opponents control. Damage and effects that say "destroy" don't destroy it.)