Lands are unique because they are 'played' but not 'cast'
The more redundancy you have on early-game acceleration, the more reliably you can cast expensive cards higher up on the curve
While this is already quite useful, whenever Zaxara's controller casts a spell with X in its mana cost, they create a 0/0 hydra with X +1/+1 counters on it, often making X-based spells much more effective
A Most Helpful Weaver Abuelo's Awakening Abyssal Harvester Activated Sleeper Adaptive Automaton Adrestia Aerial Modification Aggressive Symbiosis Alien Symbiosis Angelic Destiny Anikthea, Hand of Erebos Animate Spell (playtest) Answered Prayers Antarctic Research Base Applied Aeronautics Applied Geometry Aquitect's Will Arbiter of the Ideal Archangel Elspeth Argent Mutation Ascent of the Worthy Ashes of the Fallen Ashiok, Nightmare Weaver Ashnod's Transmogrant Assemble from Parts Astrologian's Planisphere Auto-Key Auton Soldier Avatar Destiny Awakened Skyclave Bard's Bow Bello, Bard of the Brambles Black Mage's Rod Bloodbat Summoner Blue Mage's Cane Breach the Multiverse Brenard, Ginger Sculptor Brotherhood Regalia Butch DeLoria, Tunnel Snake Cactarantula Saddle Call a Surprise Witness Call to Serve Captivating Vampire Case of the Filched Falcon Case of the Gorgon's Kiss Clavileo, First of the Blessed Coerced to Kill Coercive Recruiter Cool Fluffy Loxodon Copy Artifact Copy Land Coward // Killer Coward // Killer Curious Colossus Cursecloth Wrappings Dancer's Chakrams Dark Knight's Greatsword Daxos's Torment Deceptive Frostkite Demonic Embrace Dermotaxi Dismiss into Dream Displaced Dinosaurs Doc Ock, Evil Inventor Does Machines Dollhouse of Horrors Don Andres, the Renegade Donal, Herald of Wings Donatello, Mutant Mechanic Draconic Destiny Dragoon's Lance Drana, the Last Bloodchief
To double the number of +1/+1 counters on a creature, put a number of +1/+1 counters on it equal to the number it already has
