Blitz Automaton

Prototype {2}{R} — 3/2 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Haste

Slagwoods Bridge

Slagwoods Bridge enters the battlefield tapped.
Indestructible
{T}: Add {R} or {G}.

Geomancer's Gambit

Destroy target land. Its controller may search their library for a basic land card, put it onto the battlefield, then shuffle.
Draw a card.

Mountain

Big Score

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Rustvale Bridge

Rustvale Bridge enters the battlefield tapped.
Indestructible
{T}: Add {R} or {W}.

Ulamog's Crusher

Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents.)
Ulamog's Crusher attacks each combat if able.

Cleansing Wildfire

Destroy target land. Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffle.
Draw a card.

Unexpected Windfall

Gargadon

Trample
Suspend 4—{1}{R} (Rather than cast this card from your hand, you may pay {1}{R} and exile it with four time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)

Boarding Party

Haste
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 of your library in a random order.)

Oliphaunt

Trample
Whenever Oliphaunt attacks, another target creature you control gets +2/+0 and gains trample until end of turn.
Mountaincycling {1} ({1}, Discard this card: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.)

Dragon Breath

Enchant creature
Enchanted creature has haste.
{R}: Enchanted creature gets +1/+0 until end of turn.
When a creature with mana value 6 or greater enters the battlefield, you may return Dragon Breath from your graveyard to the battlefield attached to that creature.