Squash

This spell costs {3} less to cast if you control a Giant.
Squash deals 6 damage to target creature or planeswalker.

Cyclone Summoner

When Cyclone Summoner enters, if you cast it from your hand, return all permanents to their owners' hands except for Giants, Wizards, and lands.

Doomskar Titan

When Doomskar Titan enters, creatures you control get +1/+0 and gain haste until end of turn.
Foretell {4}{R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Tundra Fumarole

Tundra Fumarole deals 4 damage to target creature or planeswalker. Add {C} for each {S} spent to cast this spell. Until end of turn, you don't lose this mana as steps and phases end. ({S} is mana from a snow source.)

Quakebringer

Your opponents can't gain life.
At the beginning of your upkeep, Quakebringer deals 2 damage to each opponent. This ability triggers only if Quakebringer is on the battlefield or if Quakebringer is in your graveyard and you control a Giant.
Foretell {2}{R}{R}

Surtland Flinger

Whenever Surtland Flinger attacks, you may sacrifice another creature. When you do, Surtland Flinger deals damage equal to the sacrificed creature's power to any target. If the sacrificed creature was a Giant, Surtland Flinger deals twice that much damage instead.

Giant's Amulet

When Giant's Amulet enters, you may pay {3}{U}. If you do, create a 4/4 blue Giant Wizard creature token, then attach Giant's Amulet to it.
Equipped creature gets +0/+1 and has "This creature has hexproof as long as it's untapped." (It can't be the target of spells or abilities your opponents control.)
Equip {2}

Frostpyre Arcanist

This spell costs {1} less to cast if you control a Giant or a Wizard.
When Frostpyre Arcanist enters, search your library for an instant or sorcery card with the same name as a card in your graveyard, reveal it, put it into your hand, then shuffle.

Mountain

Volatile Fjord

({T}: Add {U} or {R}.)
Volatile Fjord enters tapped.

Snow-Covered Mountain

Fire Giant's Fury

Target Giant you control gets +2/+2 and gains trample until end of turn. Whenever it deals combat damage to a player this turn, exile that many cards from the top of your library. Until the end of your next turn, you may play those cards.

Basalt Ravager

When Basalt Ravager enters, it deals X damage to any target, where X is the greatest number of creatures you control that have a creature type in common.

Aegar, the Freezing Flame

Whenever a creature or planeswalker an opponent controls is dealt excess damage, if a Giant, Wizard, or spell you controlled dealt damage to it this turn, draw a card.

Berg Strider

When Berg Strider enters, tap target artifact or creature an opponent controls. If {S} was spent to cast this spell, that permanent doesn't untap during its controller's next untap step. ({S} is mana from a snow source.)

Calamity Bearer

If a Giant source you control would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Giant's Grasp

Enchant Giant you control
When Giant's Grasp enters, gain control of target nonland permanent for as long as Giant's Grasp remains on the battlefield.

Crush the Weak

Crush the Weak deals 2 damage to each creature. If a creature dealt damage this way would die this turn, exile it instead.
Foretell {R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Snow-Covered Island

Glimpse the Cosmos

Look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.
As long as you control a Giant, you may cast Glimpse the Cosmos from your graveyard by paying {U} rather than paying its mana cost. If you cast Glimpse the Cosmos this way and it would be put into your graveyard, exile it instead.

Battle of Frost and Fire

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Battle of Frost and Fire deals 4 damage to each non-Giant creature and each planeswalker.
II — Scry 3.
III — Whenever you cast a spell with mana value 5 or greater this turn, draw two cards, then discard a card.

Surtland Elementalist

As an additional cost to cast this spell, reveal a Giant card from your hand or pay {2}.
Whenever Surtland Elementalist attacks, you may cast an instant or sorcery spell from your hand without paying its mana cost.

Surtland Frostpyre

Surtland Frostpyre enters tapped.
{T}: Add {R}.
{2}{U}{U}{R}, {T}, Sacrifice Surtland Frostpyre: Scry 2. Surtland Frostpyre deals 2 damage to each creature. Activate only as a sorcery.

Invasion of the Giants

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Scry 2.
II — Draw a card. Then you may reveal a Giant card from your hand. When you do, Invasion of the Giants deals 2 damage to target opponent or planeswalker.
III — The next Giant spell you cast this turn costs {2} less to cast.

Hall of Storm Giants

If you control two or more other lands, Hall of Storm Giants enters tapped.
{T}: Add {U}.
{5}{U}: Until end of turn, Hall of Storm Giants becomes a 7/7 blue Giant creature with ward {3}. It's still a land. (Whenever it becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)