Blue has a bunch of cards that are in-jokes to the development process of the game, because, well, Blue is the 'smart' colour, right
When this creature enters, clash with an opponent
Selvala's last ability is a mana ability
Its only downside is its mana cost , which can be restrictive in multicolor decks

Release date: 2017-07-25 Alms Collector Balan, Wandering Knight Curse of Vitality Fortunate Few Kindred Boon Scalelord Reckoner Stalking Leonin Teferi's Protection Curse of Verbosity Galecaster Colossus Kindred Discovery Magus of the Mind Portal Mage Bloodline Necromancer Boneyard Scourge Curse of Disturbance Kheru Mind-Eater Kindred Dominance New Blood Patron of the Vein Vindictive Lich Bloodsworn Steward Crimson Honor Guard Curse of Opulence Disrupt Decorum Izzet Chemister Kindred Charge Shifting Shadow Territorial Hellkite Curse of Bounty Hungry Lynx Kindred Summons Qasali Slingers Traverse the Outlands Arahbo, Roar of the World Edgar Markov Fractured Identity Inalla, Archmage Ritualist Kess, Dissident Mage Licia, Sanguine Tribune Mairsil, the Pretender Mathas, Fiend Seeker Mirri, Weatherlight Duelist Nazahn, Revered Bladesmith O-Kagachi, Vengeful Kami Taigam, Ojutai Master Taigam, Sidisi's Hand The Ur-Dragon Wasitora, Nekoru Queen Bloodforged Battle-Axe Hammer of Nazahn Heirloom Blade Herald's Horn Mirror of the Forebears Ramos, Dragon Engine Path of Ancestry Blind Obedience Condemn Divine Reckoning Fell the Mighty Jareth, Leonine Titan Jazal Goldmane Kemba, Kha Regent Leonin Arbiter Leonin Relic-Warder Leonin Shikari Orator of Ojutai Oreskos Explorer Raksha Golden Cub Return to Dust Rout Seht's Tiger

In a set like Crimson Vow, that's almost good enough as it is, but there's more