So I don’t want to go the infinite combo route, or the uber-heavy control route, but I do want to maximize the value of the -1 ability by untapping lots of things each turn, so where does that leave us? Well, frankly there’s lots of options, really. We just have to dig a bit to see what’s there. Look at the existing cards in the deck, and just think about what random cards come to mind that you’d like to add.
And Tomya is targeted, so you can just target yourself to double your current hand size, or if you have Consecrated Sphinx out, you can target an opponent with a full grip, and whatever they’re drawing, you are going to draw twice as much! Watch out for instant-speed removal, though, or you’ll have just given someone a bunch of free cards for nothing!
Another card to consider in this build is Trade Routes. Basically giving all your lands Cycling 1 is pretty sweet, and there’s probably some variation on the deck that makes the ability to bounce your own lands relevant as well. Maybe with Land Equilibrium? I don’t know, that’s probably unlikely to work, and probably highly annoying if it does work. Anyway, Trade Routes is cool, so I’d consider it here.
Hmm, let's see... what else is Blue good at doing? Stealing things, and copying things; that's two. Both stealing and copying, as major themes, have been done, of course. Neither of these "themes" is deep enough or interesting enough to focus an entire deck around, in my opinion. Nonetheless they are among Blue's strengths, and both give us access, via other players' cards, to abilities and effects we might not otherwise have access to. For example, cloning another player's Acidic Slime to kill an enchantment, or "borrowing" an opposing Serra Ascendant for some lifegain. Point being, Blue is the best color for using your enemies' own cards against them. Not tapping into some of that power just wouldn't make sense.
There are a ton of options in both categories, so it's pretty much up to personal taste and/or card availability. But my recommendations tend towards the proven, time-tested methods. Obviously with as many various mana rocks and other artifacts in the deck, Phyrexian Metamorph is one of the best out there. Similarly, the new Clever Impersonator is quite versatile. One thing Blue can't do, typically, is "reanimation", but again, Planar Chaos's "what-if" color pie comes to the rescue, with Body Double, a brilliant little card. Cloning things from the graveyard is Blue's version of a Zombify, which is pretty clever. Vesuvan Shapeshifter is a fine pick if you want keep some of the Morph stuff intact, or if you just want to complete the "pickles lock" with the Brine Elemental already included.
On the stealing side of things, Bribery and Treachery are the most generic and obvious options, but folks, they are ubiquitous for a reason - they're GOOD! Like, really, really good. But if you want to avoid the cliche choices, maybe there are other options. Helm of Possession is pretty good, but I'd only really recommend this one if you have a lot of expendable utility dorks to sac. Another potentially techy pick is Chamber of Manipulation. You should easily be drawing enough cards to discard to it, but the real problem is figuring out how to use the stolen creatures, since you only get them until EOT, but they don't get haste! One possible option is to use Proteus Staff on the borrowed creature - it'll go back to the bottom of it's owner's library, but YOU still get to dig for a creature to put into play! Otherwise, Greaves and Boots can just enable haste to allow you to attack.
One of the best options, though, is Vedalken Shackles. That card is one of the most compelling reasons for me to broaden my horizons into mono-colored territories - because I've had a couple of copies sitting around for years, but never really got to use them because, well, they're pretty crap in most multicolor decks.
One of my favorite new cards in this deck is Domineering Will, which I'd definitely keep around. Blatant Thievery is kind of like a permanent version of Domineering Will, but it can steal ANYTHING! Planeswalkers, Enchantments, Lands... pretty much anything not tied down with Hexproof or Shroud is up for grabs. Reins of Power is well-known and loved by many in the format, and last year's C13 had the fantastic Illusionist's Gambit, which is a card that, every time I cast it in a game, causes me to think " holy crap, is this card actually real?!"
While Illusionist's Gambit doesn't actually say "gain control" or anything similar to that, I still put it in this section because what the card basically does is to "steal" someone else's combat phase! True, you don't get to pick the opponent to be the recipient of the misdirected attack, but basically, the card feels like it started out as a card someone designed as a joke - "gain control of target attack phase". Like, maybe it was an unused design for the third Un-set, and R&D just decided, for shits and giggles, to see if they could make a card that was functionally the same, but would actually work in real Magic, and thus Illusionist's Gambit was born.
Anyway, on the ever-shortening list of things Blue CAN'T steal, we can scratch off "combat phase".
One more thing Blue mages tend to love is their Trinket Mage packages. I threw him in mainly just to find my Sol Ring or Tormod's Crypt more consistently (Crypt has been surprisingly relevant and useful - I'd love to cut it, but it keeps proving valuable). But almost any of the variations on this deck we've discussed has a very high potential to burn through it's library and fill up the graveyard at an alarming rate. So, I'd suggest Elixir of Immortality as one option. Yes, it's mostly one of those noob cards - it doesn't actually DO anything, it gains life... but a bit of lifegain is actually kinda nice to have in a pinch, especially when it's just a bonus tacked on to another effect we already want.
Not a Trinket Mage target, but I'd also suggest Time Spiral for basically any version of this build except the version that wants to deck everyone.
There are tons of trinkets for the mage to fetch, but I generally just like to have a few that I'm really likely to want, and not a bunch of highly circumstantial effects that just clutter up my decklist. And I've already mentioned Voltaic Key previously, but here again it seems well worth mentioning. There will almost always be valid targets for the Key to untap.
And, I think, the last thing I want to talk about is defense. We've already talked about bounce spells, but Blue's other signature defensive move is to "freeze" things, I.E. tapping things down and keeping them tapped for a turn. See Frost Titan and Breaching Leviathan for examples. Other things that do this include: Tamiyo the Moon Sage, Sleep, Frost Breath, Icy Blast, and Sudden Storm. I like Tamiyo in general because she's just really good on her own, but she's also pretty good with these other effects. Using her -2 after resolving a Sleep or Breaching Leviathan, for instance, can be quite the coup.
I don't really like the "tap two guys" options much, unless I'm playing 1v1 pretty exclusively. In a multiplayer setting it'll be often that there are more than two significant threats at one time, and something like Frost Breath won't quite get there. Icy Blast and Sleep both seem like great options, though. I especially like Sleep since it's a 4-mana spell making it a great follow-up play to casting Teferi for the first time. However it, too, targets a specific opponent, so sometimes it won't be able to handle all possible threats. With all the big sea monsters and sphinxes, Icy Blast seems like it'd almost always be Ferocious.
Well, I've just about exhausted my well of ideas for this deck, but it continues to impress and inspire me the more I play it. I really didn't think the initial list was all that interesting or exciting, but I've really come around to see that there is clearly a lot of potential for the deck, and for Teferi himself.
In the end, I actually couldn't choose one direction to go in, so I just borrowed some of the ideas from all the variations I discussed above. That makes the list look a little more generic and good-stuff-ish than I'd have liked, but the deck actually plays very cohesively and has lots of little interactions and synergies that justify most of the more staple-ish inclusions. There are, as always, a handful of cards I'd love to include but couldn't find room for, or didn't have copies of available for use. But for now, here's the list I've been rocking, and it's been a blast to play.
Teferi, Temporal Archmage
Thassa, God of the Sea
Sphinx of Uthun
Scourge of Fleets
Lorthos, the Tidemaker
Call to Mind
Rite of Replication
Jace, the Mind Sculptor
Rush of Knowledge
Tamiyo, the Moon Sage
Flow of Ideas
Well of Ideas
Stroke of Genius
Elixer of Immortality
Nykthos, Shrine to Nyx
So, that's the list. I'd obviously recommend going the Snow-basic route if you have them, if you want to use the Extraplanar Lens with minimal risk, but I didn't happen to have enough on hand to do that. I'm also considering cutting Tec Edge and Halimar Depths and going back to basic Islands because I want to make sure my Vedalken Shakles, Flow of Ideas and Scourge of Fleets are as consistent as possible.
Two cards I mentioned and really wanted to add, but couldn't find any unused copies are Time Spiral and Mimic Vat. I really think those two are more or less essential here, but I'll have to pull one of each from existing decks, so figuring out which decks can live withou them is a chore I just haven't found time for yet.
I also really want Body Double in here, but haven't figured out what to cut. Geralf or Reef Worm actually feel like they're slightly underachieving in this build, so those could go, but I like using new cards, and don't have other homes waiting on them just yet, so I'm hesitant to cut them.
Chasm Skulker is one I think I forgot to mention earlier, but with the absurd number of cards this deck draws most of the time, it seemed like a natural fit. I also forgot to mention Dungeon Geists in the tap-things-down section, but it's new enough to probably have occurred to most of you anyway.
Lorthos has yet to do anything impressive for me, but I'm continuing to hold out hope that he'll prove useful at somepoint. If not, he'll be on the chopping block the minute WotC prints a new, playable Leviathan or Kraken.
Diluvian Primordial was another "good stuff" card, but I can't help but like the Primordials, and this one is another way to use opponents' spent utility spells to deal with things Blue can't normally deal with.
And I did break my group's "no countermagic" truce for a Cryptic Command, but we've pretty much all fudged this rule once or twice, when it makes sense, and here it's not always going to be a counterspell. I think it's almost as likely to be "tap your guys, draw" as it is to be "counter that, draw", and even the bounce mode isn't irrelevant here.
I did spend some time looking at Inundate, a near-forgotten gem from Eventide. Well, I don't know if "gem" is the right word, but if it's going to be played, a monoblue deck seems like the only logical place for it. Yet, somehow I can't seem to fit it in, and I'm not super convinced I need to.
And, finally, I don't like running Pongify without it's functional twin Rapid Hybridization, but so far I haven't found room for that either. In fact, I've come close to cutting Pongify, because of the few times I'd had it in hand, but the 3/3 token it leaves behind actually posed a threat to Teferi so I couldn't use it! But at the same time, having a cheap, instant-speed answer to hasty threats like Akroma, or game-breaking bombs like Consecrated Sphinx (in the hands of the enemy, at least), seems very necessary, so again I kind of want both!
Okay, now I really have run out of ideas to throw at you, so I'm done. I hope this gives you some fodder for your own renovations and redesigns. As alwasy, I appreciate feedback, so let me know what hidden gems I've overlooked, or even if I missed something that should have been pretty obvious!