Kodama of the Center Tree

Kodama of the Center Tree's power and toughness are each equal to the number of Spirits you control.
Kodama of the Center Tree has soulshift X, where X is the number of Spirits you control. (When this creature dies, you may return target Spirit card with mana value X or less from your graveyard to your hand.)

Haru-Onna

When Haru-Onna enters, draw a card.
Whenever you cast a Spirit or Arcane spell, you may return Haru-Onna to its owner's hand.

Forest

Lifespinner

{T}, Sacrifice three Spirits: Search your library for a legendary Spirit permanent card, put it onto the battlefield, then shuffle.

Rending Vines

Destroy target artifact or enchantment if its mana value is less than or equal to the number of cards in your hand.
Draw a card.

Unchecked Growth

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

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.)

Long-Forgotten Gohei

Arcane spells you cast cost {1} less to cast.
Spirit creatures you control get +1/+1.

Sekki, Seasons' Guide

Sekki, Seasons' Guide enters with eight +1/+1 counters on it.
If damage would be dealt to Sekki, prevent that damage, remove that many +1/+1 counters from Sekki, and create that many 1/1 colorless Spirit creature tokens.
Sacrifice eight Spirits: Return Sekki from your graveyard to the battlefield.

Petalmane Baku

Whenever you cast a Spirit or Arcane spell, you may put a ki counter on Petalmane Baku.
{1}, Remove X ki counters from Petalmane Baku: Add X mana of any one color.

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.

Loam Dweller

Whenever you cast a Spirit or Arcane spell, you may put a land card from your hand onto the battlefield tapped.

Forked-Branch Garami

Soulshift 4, soulshift 4 (When this creature dies, you may return up to two target Spirit cards with mana value 4 or less from your graveyard to your hand.)