When cast, they enter the battlefield with their battle side face up, and its controller chooses an opponent to be that battles protector

Creature (27) 1x Akroan Crusader 1x Akroan Hoplite 1x Archetype of Courage 1x Balefire Liege 1x Benalish Commander 1x Boros Swiftblade 1x Brimaz, King of Oreskos 1x Captain of the Watch 1x Catapult Master 1x Darien, King of Kjeldor 1x Daru Warchief 1x Field Marshal 1x Gisela, Blade of Goldnight 1x Goldnight Commander 1x Hearthfire Hobgoblin 1x Hero of Bladehold 1x Hero of Oxid Ridge 1x Iroas, God of Victory *list* 1x Legion Loyalist 1x Odric, Master Tactician 1x Phalanx Leader 1x Preeminent Captain 1x Soldier of the Pantheon 1x Sun Titan 1x Sunhome Guildmage 1x Veteran Swordsmith Land (39) Enchantment (8) 1x Assemble the Legion 1x Cage of Hands 1x Cathars' Crusade 1x Dictate of Heliod 1x Glorious Anthem 1x Leyline of the Meek 1x Light from Within 1x Marshal's Anthem Artifact (10) Instant (13) 1x Accelerate 1x Ajani's Presence 1x Apostle's Blessing 1x Boros Charm 1x Carom 1x Coordinated Assault 1x Crimson Wisps 1x Defiant Strike 1x Faith's Reward 1x Gods Willing 1x Guided Strike 1x Raise the Alarm 1x Swift Maneuver

I find it fun to crunch my brain and find the fastest way to assemble my deck's combo
To ensure this list is as accommodating and inclusive as possible, all of these cards are around $5 or less
Based on the latest market prices tracked on TCG Stacked, Loot, the Key to Everything is worth about $2.96 USD for a regular copy and $4.19 USD for a foil copy
This comes off the back of Battle for Zendikar block, which was all about the other two Eldrazi Titans, Ulamog and Kozilek