Mercy Killing

Target creature's controller sacrifices it, then creates X 1/1 green and white Elf Warrior creature tokens, where X is that creature's power.

Leyline of Abundance

If this card is in your opening hand, you may begin the game with it on the battlefield.
Whenever you tap a creature for mana, add an additional {G}.
{6}{G}{G}: Put a +1/+1 counter on each creature you control.

Plains

Craterhoof Behemoth

Haste
When this creature enters, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Fresh Meat

Create a 3/3 green Beast creature token for each creature put into your graveyard from the battlefield this turn.

Harmonize

Devoted Druid

{T}: Add {G}.
Put a -1/-1 counter on this creature: Untap this creature.

Forest

Quillspike

{B/G}, Remove a -1/-1 counter from a creature you control: This creature gets +3/+3 until end of turn.

Vizier of Remedies

If one or more -1/-1 counters would be put on a creature you control, that many -1/-1 counters minus one are put on it instead.

Chord of Calling

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle.