Scourge of Valkas

Flying
Whenever this creature or another Dragon you control enters, it deals X damage to any target, where X is the number of Dragons you control.
{R}: This creature gets +1/+0 until end of turn.

Spaghetti Junction

{T}: Add {C}
{4}, {T}: Create a 3/2 colorless Vehicle artifact token with crew 1.
Whenever a Vehicle you control attacks, put a traffic counter on this land.
When this land has eight traffic counters on it, sacrifice it. If you do, create Atlantakul, a legendary 20/20 colorless Eldrazi creature token with annihilator 2.

Sylvan Offering

Choose an opponent. You and that player each create an X/X green Treefolk creature token.
Choose an opponent. You and that player each create X 1/1 green Elf Warrior creature tokens.

Forest

Sliver Legion

All Sliver creatures get +1/+1 for each other Sliver on the battlefield.

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of this creature.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Shared Summons

Search your library for up to two creature cards with different names, reveal them, put them into your hand, then shuffle.

The Ur-Dragon

Eminence — As long as The Ur-Dragon is in the command zone or on the battlefield, other Dragon spells you cast cost {1} less to cast.
Flying
Whenever one or more Dragons you control attack, draw that many cards, then you may put a permanent card from your hand onto the battlefield.