Mountain (253) [Theros Beyond Death]Set: Theros Beyond Death Type: Basic Land Mountain Rarity: Common ({T}: Add {R}.)

Set: Visions Type: World Enchantment Rarity: Rare Cost: {3}{W} When Eye of Singularity enters the battlefield

Set: Battle for Zendikar Type: Enchantment Rarity: Rare Cost: {4}{U} Converge — Prism Array enters the battlefield with a crystal counter on it for each color of mana spent to cast it

Set: Fourth Edition Type: Artifact Rarity: Rare Cost: {2} {3}

Set: HeartGold & SoulSilver: Triumphant Type: Psychic Rarity: Common Retreat cost: Colorless

Set: Commander 2013 Type: Instant Rarity: Rare Cost: {2}{R}{R} You may choose new targets for target instant or sorcery spell

Set: Commander 2011 Type: Land Rarity: Common {T}: Add one mana of any color in your commander's color identity

and thinks

Set: Commander 2019 Type: Enchantment Rarity: Rare Cost: {3}{U} Instant and sorcery spells you cast cost {1} less to cast

Set: Urza's Destiny Type: Artifact Rarity: Uncommon Cost: {3} Whenever a creature attacks

not unlike some admirable designs I have seen here

but all feel bound to answer the call of the horn

Set: Magic 2013 Type: Creature — Hydra Rarity: Mythic Cost: {X}{G}{G} Primordial Hydra enters the battlefield with X +1/+1 counters on it