Blind-Spot Giant

Blind-Spot Giant can't attack or block unless you control another Giant.

Borderland Behemoth

Trample
Borderland Behemoth gets +4/+4 for each other Giant you control.

Obsidian Battle-Axe

Equipped creature gets +2/+1 and has haste.
Whenever a Warrior creature enters the battlefield, you may attach Obsidian Battle-Axe to it.
Equip {3}

Ancient Amphitheater

As Ancient Amphitheater enters the battlefield, you may reveal a Giant card from your hand. If you don't, Ancient Amphitheater enters the battlefield tapped.
{T}: Add {R} or {W}.

Crush Underfoot

Choose a Giant creature you control. It deals damage equal to its power to target creature.

Hamletback Goliath

Whenever another creature enters the battlefield, you may put X +1/+1 counters on Hamletback Goliath, where X is that creature's power.

Pyretic Ritual

Stinkdrinker Daredevil

Giant spells you cast cost {2} less to cast.

Rugged Prairie

{T}: Add {C}.
{R/W}, {T}: Add {R}{R}, {R}{W}, or {W}{W}.

Hammerfist Giant

{T}: Hammerfist Giant deals 4 damage to each creature without flying and each player.

Vessel of Volatility

{1}{R}, Sacrifice Vessel of Volatility: Add {R}{R}{R}{R}.

Hundred-Handed One

Vigilance
{3}{W}{W}{W}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
As long as Hundred-Handed One is monstrous, it has reach and can block an additional ninety-nine creatures each combat.

Sunrise Sovereign

Other Giant creatures you control get +2/+2 and have trample.

Mountain

Clifftop Retreat

Clifftop Retreat enters the battlefield tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

Desolation Giant

Kicker {W}{W} (You may pay an additional {W}{W} as you cast this spell.)
When Desolation Giant enters the battlefield, destroy all other creatures you control. If it was kicked, destroy all other creatures instead.

Boros Signet

Brion Stoutarm

Lifelink
{R}, {T}, Sacrifice another creature: Brion Stoutarm deals damage equal to the sacrificed creature's power to target player or planeswalker.

Kalemne, Disciple of Iroas

Double strike, vigilance
Whenever you cast a creature spell with mana value 5 or greater, you get an experience counter.
Kalemne, Disciple of Iroas gets +1/+1 for each experience counter you have.