Ivy Lane Denizen

Whenever another green creature you control enters, put a +1/+1 counter on target creature.

Squirrel Nest

Enchant land
Enchanted land has "{T}: Create a 1/1 green Squirrel creature token."

Squirrel Sovereign

Squirrel Mob

Squirrel Mob gets +1/+1 for each other Squirrel on the battlefield.

Thriving Grove

Thriving Grove enters tapped. As it enters, choose a color other than green.
{T}: Add {G} or one mana of the chosen color.

Scurry Oak

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever one or more +1/+1 counters are put on Scurry Oak, you may create a 1/1 green Squirrel creature token.

Forest

Deep Forest Hermit

Vanishing 3 (This creature enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When Deep Forest Hermit enters, create four 1/1 green Squirrel creature tokens.
Squirrels you control get +1/+1.

Squirrel Sanctuary

When Squirrel Sanctuary enters, create a 1/1 green Squirrel creature token.
Whenever a nontoken creature you control dies, you may pay {1}. If you do, return Squirrel Sanctuary to its owner's hand.

Chitterspitter

At the beginning of your upkeep, you may sacrifice a token. If you do, put an acorn counter on Chitterspitter.
Squirrels you control get +1/+1 for each acorn counter on Chitterspitter.
{G}, {T}: Create a 1/1 green Squirrel creature token.

Scurrid Colony

Reach
Scurrid Colony gets +2/+2 as long as you control eight or more lands.

Might of the Masses

Target creature gets +1/+1 until end of turn for each creature you control.

Chatter of the Squirrel

Create a 1/1 green Squirrel creature token.
Flashback {1}{G} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Beast Within

Destroy target permanent. Its controller creates a 3/3 green Beast creature token.