Two-Headed Sliver

All Sliver creatures have menace. (They can't be blocked except by two or more creatures.)

Forest

Sliver creatures you control have "Whenever this creature is dealt damage, it deals that much damage to target player or planeswalker."

Target creature gets +3/+3 until end of turn.

Sliver creatures you control have "{T}, Discard a card: Draw a card."

Sliver creatures you control have "Whenever this creature deals combat damage to a player, put a +1/+1 counter on it."

Sliver creatures you control have deathtouch. (Any amount of damage a creature with deathtouch deals to a creature is enough to destroy it.)

Whenever a Sliver becomes blocked, that Sliver gets +1/+1 until end of turn for each creature blocking it.

Magma Jet deals 2 damage to any target. Scry 2.

Rugged Highlands enters tapped.
When Rugged Highlands enters, you gain 1 life.
{T}: Add {R} or {G}.

Changeling (This card is every creature type.)

All Sliver creatures have haste.
All Slivers have "{1}, Sacrifice this permanent: Target Sliver creature gets +2/+2 until end of turn."

Sliver creatures you control have first strike. (They deal combat damage before creatures without first strike.)