Even without taking color requirements into effect, a lot of Dragons cost a lot of mana
Have fun, nerd
You get to draw cards until you have six in your hand and you have the option of discarding a card
If the card you tutor up is four mana value or less and you bargained the spell, you can choose to cast it from exile FOR FREE
Ill try to cover, whenever it fits, cards that are most subject to alteration in price

Aberrant Researcher Admiral Brass, Unsinkable Advanced Reconstruction Airlift Chaplain Altar of the Wretched Angel of Suffering Another Chance Anowon, the Ruin Thief Argoth, Sanctum of Nature Ark of Hunger Armored Skaab Ashcoat of the Shadow Swarm Ashcoat of the Shadow Swarm Atrocious Experiment Aven Heartstabber Ballad of the Black Flag Bane-Marked Leonin Barrowgoyf Belltower Sphinx Billowing Shriekmass Black Widow, Daring Operative Blight Titan Blood Spatter Analysis Bloodcurdler Bruvac the Grandiloquent Carrion Cruiser Carrion Grub Cauldron's Gift Cemetery Tampering Cephalid Aristocrat Cephalid Illusionist Cephalid Vandal Chains of Mephistopheles Charmed Pendant Cloudhoof Kirin Combustible Gearhulk Convergence of Dominion Coral Colony Corpse Churn Court of Cunning Covetous Castaway Crow of Dark Tidings Daggerfang Duo Dakmor Salvage Darkblast Dawnhand Eulogist Deathcap Marionette Deep Spawn Demogorgon's Clutches Demonic Covenant Deranged Assistant Devoted Grafkeeper Devourer of Memory Dig Up the Body Diviner of Mist Does Machines Doom's Servo-Guards Doombot Harbinger Dread Osseosaur Dread Summons Dreadhound Eden, Seat of the Sanctum Eerie Gravestone Eerie Soultender Emry, Lurker of the Loch Ertai's Familiar Excavated Wall Extract from Darkness Extractor Demon Eyeblight Cullers Fallaji Archaeologist False Memories
