When Urza enters, create a 0/0 colorless Construct artifact creature token with "This token gets +1/+1 for each artifact you control."
Tap an untapped artifact you control: Add .
: Shuffle your library, then exile the top card. Until end of turn, you may play that card without paying its mana cost.

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Sliver spells you cast have cascade.

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 this creature enters, create four 1/1 green Squirrel creature tokens.
Squirrels you control get +1/+1.

Delve (Each card you exile from your graveyard while casting this spell pays for .)
Magmatic Sinkhole deals 5 damage to target creature or planeswalker.