Instant speed cloning!
This is a bit of gimmick deck which I built a while ago, with a few updates from set to set. I've never really tested it, and I suspect it will be terrible, but I liked the idea (edit: I've played 5-6 games and it won a couple!) (edit edit: turns out this deck isn't bad!) (edit edit edit: this might be my favourite deck).
The first limb of the deck strategy is, of course, polymorphing. The core of many blue and/or red polymorph decks is to have a limited amount of high impact targets (maybe only one), so that polymorph basically functions as a tutor for your win-con. However, you also need targets to polymorph - probably your commander, or tokens or man-lands which can't also be flipped instead of your win-con. Jalira, Master Polymorphist has a very specifically worded polymorph ability - it can only find "nonlegendary" creatures. That means that, instead of filling up your deck with token generators or man-lands, you can fill it up with high utility, cheap blue legendary creatures, and make sure your win-cons are nonlegendary (e.g. Blightsteel Colossus). Of course, it doesn't hurt to have some of those man-lands and token generators as well.
However, I find single target polymorph decks a little boring - you're obviously going to play them the same way every game. I also wanted to go all in on the shapechange theme. As such, every target for Jalira's ability in this deck is itself a cloning creature. The idea is that you can copy any creature on the battlefield at instant speed using her ability (including ETB effects) for a kind of flexible aikido strategy.
Finally, the spells. Any blue deck will benefit from the usual counterspell and card draw suite. You can play that here. As I was building to a theme, I've only included a few of those cards. Instead, most of the spell support is instants, sorceries or auras with a shapechange effect. They keep printing more, but I think I have most of the good ones (Polymorph itself is just too expensive to cast). The result is a mono-blue deck that has little to no counterspells, but is oddly strong on removal and combat tricks, which I quite like.
You may wonder what the win-con is. You would be right to wonder. Best case scenario, they play something big and impactful, you copy it and then turn theirs into a frog. Bonus points if you do it all during combat and then block their frog. You can also really mess with combat between other players! It sounds risky, but it suits almost any table and makes for a different experience every game. You might be surprised how often your opponents unwittingly give you the tools to defeat them. That said, I have definitely killed people with clones of Inkmoth Nexus more often than you would think (especially when someone plays a Coat of Arms).
A few things to note:
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Jalira, Master Polymorphist does not actually target, which works well with a few of your legendary creatures that make your creatures hard to target, notably Kira, Great Glass-Spinner.
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There are not actually that many clones in the deck, which could be a problem if you actually have to use the ability a lot in a game. A few are reusable, but there is also a "shuffle your graveyard into your library" card, Cranial Archive, which doubles as a kind of graveyard hate against opponents. Not sure what the right balance is but I'm yet to have a problem. You could perhaps run less legendary creatures and more clones (e.g. Quicksilver Gargantuan, Clone), or one of the Eldrazi that shuffles your graveyard in (you won't be able to hit it with Jalira).
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A neat trick for keeping Jalira alive while she's online (which I think works?) - if someone tries to remove her, you can polymorph another creature, clone Jalira, and sacrifice the targeted one to the legend rule.
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The snow-covered islands are there because I used to run larger creatures and Extraplanar Lens as a backup plan. Still useful for Scrying Sheets, Frostwalk Bastion and Faceless Haven, but otherwise entirely replaceable.
Any new clones or cheap blue (or colourless) legendary creatures can be used to upgrade this deck, and there are a lot of existing ones which are arguably better than the ones I have chosen. Doesn't really matter which you play, as long as they are reasonably cheap and their ability isn't entirely useless! There are no doubt quite a few upgrades that can be made with existing cards (some of the mana rocks I've used here are a bit questionable in retrospect, but all my best ones are in other decks) (edit: the mana rocks are getting better!). If you ever try this or a similar strategy, let me know what key support cards I'm missing or what the best ratio of clones to polymorph targets is!
Updates 13/1/21: Cards added: Malcolm, Keen-Eyed Navigator, Esior, Wardwing Familiar, Sakashima of a Thousand Faces, Rhystic Study. Cards removed: Barrin, Master Wizard, Vendilion Clique, Callaphe, Beloved of the Sea, Mystic Remora.
Updates 17/3/21: Cards added: Faceless Haven, Ravenform, Cosima, God of the Voyage
. Cards removed: Scrying Sheets, Mana Drain, Rayne, Academy Chancellor.
Updates 6/9/21: Cards added: True Polymorph, Grazilaxx, Illithid Scholar. Cards removed: Force of Will, Cosima, God of the Voyage
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Updates 7/12/21: Cards added: Jacob Hauken, Inspector
. Cards removed: Baral, Chief of Compliance.
Updates 2/4/22: Cards added: The Reality Chip. Cards removed: Malcolm, Keen-Eyed Navigator.
Updates 26/6/22: Cards added: Volo, Itinerant Scholar, Alora, Merry Thief, Gale, Waterdeep Prodigy, Mirrorhall Mimic
, Undercover Operative. Cards removed: The Reality Chip, Quicksilver Gargantuan, Elixir of Immortality, Alirios, Enraptured, Emry, Lurker of the Loch.
Updates 27/8/22: Cards added: Baral, Chief of Compliance. Cards removed: Volo, Itinerant Scholar.
Updates 14/1/23: Cards added: Resculpt, Mystic Reflection, Otawara, Soaring City, Pirated Copy, Hurkyl, Master Wizard, In Too Deep, Mishra's Foundry. Cards removed: Capsize, Cryptic Command, Snow-Covered Island, Gigantoplasm, Gale, Waterdeep Prodigy, Muddle the Mixture, Reliquary Tower.
Updates 25/2/23: Cards added: Witness Protection, Drafna, Founder of Lat-Nam, Scrying Sheets, Scavenger Grounds, Polymorphous Rush, Mirrex, Gigantoplasm. Cards removed: Ichthyomorphosis, Zhuge Jin, Wu Strategist, Snow-Covered Island, Springjack Pasture, Mystic Remora, Mishra's Foundry, Mercurial Pretender (apparently it took me this long to realise Mercurial Pretender had the "creature you control" text).
Updates 22/4/23: Cards added: Chronatog Totem, Soul-Guide Lantern, Dress Down, Exotic Orchard, Mirrormade, Mishra's Foundry, Mana Crypt (freed one up from another deck). Cards removed: Lady Sun, Gift of Tusks, Mobilized District, Everflowing Chalice, Zoetic Cavern, Alora, Merry Thief, Cyclonic Rift (obviously good but so boring, it's always the best play).
Updates 1/10/23: Cards added: Virtue of Knowledge. Cards removed: Mystic Remora.
