Frogs have always been my favorite animal; they need more love in Magic the Gathering to be honest. Finding a way to make this deck power level 5-7 has been difficult.
The gimmick here is to use Mairsil, the Pretender as a template for copy-token generation. Mairsil's ability to gain the activated abilities of cards in exile with cage counters, makes him (or her?) the ideal copy candidate since the goal is an army with awesome abilities. We then use Croaking Counterpart to turn him to frog.
Immediately, there are some problems, though. Firstly, duplicating Mairsil can't be done because of the legendary rule. These cards can get around that: Double Major, Helm of the Host, Spark Double, Sakashima of a Thousand Faces. We could also mutate onto Mairsil, but that would require casting Croaking Counterpart first to make the human Mairsil a frog- remember mutate doesn't work on humans. (If we do that, though, we lose the frog type, which defeats my whole goal!) Secondly, we need to have either Pack Rat or Myr Propagator in hand to cage or we won't be generating an army any time soon.
Even with all 8 of the cards listed, probabilistically speaking, one would have a %0.00168 chance of starting with Mairsil, a legendary remover, and either Pack Rat or Myr Propagator in his/her opening hand. (Notice I didn't include having Croaking Counterpart.) Of course, the opponent isn't going to just let the gimmick play out either. Someone with a removal spell would see the potential and remove it. Chances are high for some removal. To beat all these odds, there are four options (at least as far as I can figure): run lots of card draw, run lots of self-mill with recursion, run tutors, run some control or stacks pieces to slow the opponents.
Self-Duplicating Creatures:
Biowaste Blob,
Delina, Wild Mage,
Dreadfeast Demon,
Esika's Chariot as a token,
Ghired, Conclave Exile as a token,
Giant Adephage,
Krothuss, Lord of the Deep duplicated once already,
Mairsil, the Pretender + Pack Rat or Myr Propagator caged,
Mirror-Sigil Sergeant,
Mishra's Self-Replicator,
Mist-Syndicate Naga,
Myr Propagator,
Necrotic Ooze with Pack Rat or Myr Propagator in the graveyard
Ochre Jelly,
Pack Rat,
Polyraptor,
Progenitor Mimic,
Rhys the Redeemed as a token,
Scute Swarm,
Selesnya Eulogist as a token,
Sorcerer's Broom,
Spawnwrithe,
Specimen Collector with at least two,
Splitting Slime,
Sprouting Phytohydra,
Trostani, Selesnya's Voice as a token,
Vitu-Ghazi Guildmage as a token,
Wayfaring Temple as a token
Cards to Cage for Abilities
Culling Dais, Empowered Autogenerator, Golden Urn, Grindclock, Magistrate's Scepter, Lux Cannon, Perilous Vault, Shadowspear, Crystalline Crawler, Daring Apprentice, Falkenrath Aristocrat, Glen Elendra Archmage, Immersturm Predator, Lotleth Troll, Mindless Automaton, Sage of Fables, Myr Propagator, Pack Rat, Sage of Fables, Rootcoil Creeper, Siren Stormtamer, Spike Feeder, Spike Weaver, Spore Frog, Gristleback, Stingmoggie, Shauku, Endbringer, Minion of Leshrac, Tradewind Rider, Trench Behemoth, Underrealm Lich, Walking Ballista, Workhorse, Rainbow Efreet
Cards that give keyword abilities permanently
Brokkos, Apex of Forever, Nethroi, Apex of Death, Otrimi, the Ever-Playful, Snapdax, Apex of the Hunt, Vadrok, Apex of Thunder, Cavern Whisperer, Dirge Bat, Dreamtail Heron, Gemrazer, Sawtusk Demolisher, Sea-Dasher Octopus, Souvenir Snatcher, Vulpikeet, Domri Rade, Elspeth, Knight-Errant, Elspeth, Sun's Champion, Garruk, Cursed Huntsman, Vivien Reid
Cards that wheel
Commit / Memory, Dark Deal, Day's Undoing, Echo of Eons, Magus of the Jar, Magus of the Wheel, Sway of the Stars, The Great Aurora, Time Reversal, Timetwister, Windfall
Card Draw Options
Anvil of Bogardan, Beast Whisperer, Bolas's Citadel, Coiling Oracle, Culling Dais, Dryad Greenseeker, Gretchen Titchwillow, Jadelight Ranger, Lifecrafter's Bestiary, Aesi, Tyrant of Gyre Strait,
Mill Options
Charmed Pendant, Deranged Assistant, Grindclock, Hedron Crab, Hermit Druid, Jadelight Ranger, Mesmeric Orb,
Exile Removal
Angel of the Ruins, Angelic Purge, Crush Contraband, Devious Cover-Up, Dissipate, Fade into Antiquity, Faerie Trickery, Fate Forgotten, Forsake the Worldly, Ironwright's Cleansing, Merciless Eviction, Return to Dust, Revoke Existence, Summary Dismissal, Sylvan Reclamation,
Typical Tapped Mana Ramp
Blighted Woodland, Burnished Hart, Cleansing Wildfire, Cultivate, Dawntreader Elk, Deathsprout, Dire-Strain Rampage, Empowered Autogenerator, Evolving Wilds, Explorer's Scope, Explosive Vegetation, Far Wanderings, Fertilid, Font of Fertility, Frenzied Tilling, Kodama's Reach, Map the Wastes, Migration Path, Migratory Greathorn, Mwonvuli Acid-Moss, Omen of the Hunt, Path of Discovery, Rampant Regrowth, Risen Reef, Road//Ruin, Roiling Regrowth, Sakura-Tribe Elder, Scaretiller, Solemn Simulacrum, Sword of the Animist, Terramorphic Expanse, Thrasios, Triton Hero, Unexpected Results, Urban Evolution, Vastwood Surge, Wayfarer's Bauble, World Shaper, Zimone, Quandrix Prodigy
Play Additional Lands or Untapped Mana Ramp
Aesi, Tyrant of Gyre Strait, Azusa, Lost but Seeking, Broken Bond, Burgeoning, Caravan Vigil, Chulane, Teller of Tales, Coiling Oracle, Crop Rotation, Culling Ritual, Dreamscape Artist, Druidic Satchel, Dryad of the Ilysian Grove, Enter the Unknown, Escape to the Wilds, Eureka Moment, Exploration, Explore, Field of Ruin, Geomancer's Gambit, Gretchen Titchwillow, Growth Spiral, Harrow, Kiora, the Crashing Wave, Manabond, Parcelbeast, Quandrix Cultivator, Reap and Sow, Sakura-Tribe Scout, Scale the Heights, Seismic Spike, Skyward Eye Prophets, Song of Creation, Storm Cauldron, Sword of Hearth and Home, The Gitrog Monster, Unexpected Results, Urban Evolution, Uro, Titan of Nature's Wrath,
Cards that Control and (Draw or Ramp)
Angel of the Ruins, Broken Bond, Cleansing Wildfire, Culling Ritual, Deadeye Tracker, Deathsprout, Dire-Strain Rampage, Field of Ruin, Frenzied Tilling, Geomancer's Gambit, Implode, Magus of the Future, Memory Leak, Mwonvuli Acid-Moss, Natural Reclamation, Reap and Sow, Road//Ruin, Seismic Spike, Sire of Stagnation, Sylvan Reclamation, True Love's Kiss, Violent Impact, Witherbloom Command
Frog-Themed Cards
Croaking Counterpart, Fauna Shaman, Frogify, Grolnok, the Omnivore, Incubation / Incongruity, Otrimi, the Ever-Playful, Polymorphist's Jest, Rapid Hybridization, The Gitrog Monster, Tomorrow, Azami's Familiar, Trollbred Guardian, Turn to Frog, Unwilling Ingredient, Visions of Dominance
