Briarknit Kami

Whenever you cast a Spirit or Arcane spell, put a +1/+1 counter on target creature.

Island

Forest

Unchecked Growth

Target creature gets +4/+4 until end of turn. If it's a Spirit, it gains trample until end of turn.

Kami of the Hunt

Whenever you cast a Spirit or Arcane spell, Kami of the Hunt gets +1/+1 until end of turn.

Kaijin of the Vanishing Touch

Defender (This creature can't attack.)
Whenever Kaijin of the Vanishing Touch blocks a creature, return that creature to its owner's hand at end of combat. (Return it only if it's on the battlefield.)

Sire of the Storm

Flying
Whenever you cast a Spirit or Arcane spell, you may draw a card.

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.)

Elder Pine of Jukai

Whenever you cast a Spirit or Arcane spell, reveal the top three cards of your library. Put all land cards revealed this way into your hand and the rest on the bottom of your library in any order.
Soulshift 2 (When this creature dies, you may return target Spirit card with mana value 2 or less from your graveyard to your hand.)

Ideas Unbound

Draw three cards. Discard three cards at the beginning of the next end step.

Kodama of the South Tree

Whenever you cast a Spirit or Arcane spell, each other creature you control gets +1/+1 and gains trample until end of turn.

Scaled Hulk

Whenever you cast a Spirit or Arcane spell, Scaled Hulk gets +2/+2 until end of turn.

Guardian of Solitude

Whenever you cast a Spirit or Arcane spell, target creature gains flying until end of turn.

Teller of Tales

Flying
Whenever you cast a Spirit or Arcane spell, you may tap or untap target creature.