Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

Timbermaw Larva

Whenever Timbermaw Larva attacks, it gets +1/+1 until end of turn for each Forest you control.

Primeval Titan

Trample
Whenever Primeval Titan enters or attacks, you may search your library for up to two land cards, put them onto the battlefield tapped, then shuffle.

Aggressive Mammoth

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Other creatures you control have trample.

Farhaven Elf

When Farhaven Elf enters, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Forest

Blanchwood Armor

Enchant creature
Enchanted creature gets +1/+1 for each Forest you control.

Sakura-Tribe Elder

Sacrifice Sakura-Tribe Elder: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

End-Raze Forerunners

Vigilance, trample, haste
When End-Raze Forerunners enters, other creatures you control get +2/+2 and gain vigilance and trample until end of turn.

Raven Wings

Equipped creature gets +1/+0, has flying, and is a Bird in addition to its other types.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Dawntreader Elk

{G}, Sacrifice Dawntreader Elk: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.