Hero of Leina Tower

Heroic — Whenever you cast a spell that targets this creature, you may pay {X}. If you do, put X +1/+1 counters on this creature.

Wavecrash Triton

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

Battlefield Thaumaturge

Each instant and sorcery spell you cast costs {1} less to cast for each creature it targets.
Heroic — Whenever you cast a spell that targets this creature, this creature gains hexproof until end of turn.

Giggling Skitterspike

Indestructible
Whenever this creature attacks, blocks, or becomes the target of a spell, it deals damage equal to its power to each opponent.
{5}: Monstrosity 5. (If this creature isn't monstrous, put five +1/+1 counters on it and it becomes monstrous.)

Season of Growth

Whenever a creature you control enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Whenever you cast a spell that targets a creature you control, draw a card.

Silverfur Partisan

Trample
Whenever a Wolf or Werewolf you control becomes the target of an instant or sorcery spell, create a 2/2 green Wolf creature token.

Artisan of Forms

Heroic — Whenever you cast a spell that targets this creature, you may have this creature become a copy of target creature, except it has this ability.

Fugitive Druid

Whenever this creature becomes the target of an Aura spell, you draw a card.

War-Wing Siren

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

Stormchaser Drake

Flying
Whenever this creature becomes the target of a spell you control, draw a card.

Chorus of the Tides

Flying
Heroic — Whenever you cast a spell that targets this creature, scry 1. (To scry 1, look at the top card of your library, then you may put that card on the bottom.)

Triton Fortune Hunter

Heroic — Whenever you cast a spell that targets this creature, draw a card.

Setessan Oathsworn

Heroic — Whenever you cast a spell that targets this creature, put two +1/+1 counters on this creature.

Ivy, Gleeful Spellthief

Flying
Whenever a player casts a spell that targets only a single creature other than Ivy, you may copy that spell. The copy targets Ivy. (A copy of an Aura spell becomes a token.)

Centaur Battlemaster

Heroic — Whenever you cast a spell that targets this creature, put three +1/+1 counters on this creature.

Legolas, Master Archer

Reach
Whenever you cast a spell that targets Legolas, put a +1/+1 counter on Legolas.
Whenever you cast a spell that targets a creature you don't control, Legolas deals damage equal to its power to up to one target creature.

Staunch-Hearted Warrior

Meletis Astronomer

Heroic — Whenever you cast a spell that targets this creature, look at the top three cards of your library. You may reveal an enchantment card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Gnarlback Rhino

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Whenever you cast a spell that targets this creature, draw a card.

Pheres-Band Thunderhoof

Druid of Horns

Whenever you cast an Aura spell that targets this creature, create a 3/3 green Beast creature token.