1 - Staff of Eden, Vaults Key Staff of Eden, Vaults Key is the first card I want to discuss
Of course there are ways of getting cards without buying sealed
Instead of paying 1 life to tap for any color, it taps for 1 of any color of mana, with the idea that you would often suffer point of mana burn making it a slightly better City of Brass
There are three types of abilities that cards can have: Loyalty Abilities

Aesi, Tyrant of Gyre Strait Benthic Anomaly Benthic Behemoth Biolume Egg Biolume Serpent Bladecoil Serpent Bog Serpent Caetus, Sea Tyrant of Segovia Cryptic Serpent Deep-Sea Serpent Deep-Sea Terror Denizen of the Deep Dirgur Nemesis Dreamwinder Floodtide Serpent Frilled Sea Serpent Gearseeker Serpent Harbor Serpent Iceridge Serpent Junk Winder Koma, Cosmos Serpent Koma, Cosmos Serpent Koma, World-Eater Kukemssa Serpent Lava Serpent Lightning Serpent Loch Mare Lochmere Serpent Marjhan River Serpent Ronom Serpent Sandbar Serpent Scrapdiver Serpent Sea Monster Sea Serpent Serpent of Yawning Depths Serpent of the Endless Sea Serpent of the Pass Shoal Serpent Shrouded Serpent Slinking Serpent Slipstream Serpent Sliptide Serpent Spire Serpent Steelclad Serpent Striped Riverwinder Sword Coast Serpent Taniwha The Terror of Serpent's Pass The Unagi of Kyoshi Island Tolarian Serpent Tolarian Terror Verazol, the Split Current Vodalian Serpent Wormhole Serpent Xolatoyac, the Smiling Flood Yorion, Sky Nomad
