Strong/Staples:

Mischievous Mystic (U): Just a better Emrakul’s Messenger in most situations, which makes this probably the best (or certainly top-tier) Blue 2/1 flyer for 2-mana.

Interest:

Cynette, Jelly Drover (U): Talrand’s Invocation is probably stronger on its own, but this randomly anthems so many Blue creatures and tokens and it’s an inherent 3-for-1 Sad for me,but this probably replaces Wing Splicer.

Faebloom Trick (U): Two bodies is almost always better than one and this is an instant, but this doesn’t keep a creature tapped, so I think it has pros and cons versus Frost Trickster. That’s clearly playable, though.

Similar:

Refute (C): Probably more versatile than [{Exclude]], but still behind Counterspell and Mana Leak et al.

Skyship Buccaneer (U): Higher ceiling/lower floor version of Gryff Vanguard / Quicksilver Fisher, but the upside is certainly there especially if you’re supporting Blue aggro/tempo.

Unique/Synergy:

Cephalid Inkmage (U): I like the card selection, but it’s not as good as Serum Visionary and you can get mill more cheaply. I also don’t know that a 2/2 unblockable is the payoff you’re looking for in the late game. But this could be a control finisher.

Imprisoned in the Moon (U): Rare downshift. The effect isn’t super well-costed (giving your opponent ramp is worse than a lot of people think), but it’s also something that Blue doesn’t really get. I’d also point out that this can color-screw an opponent, which might not be a play pattern you want to support.

Phantasmal Shieldback (U): Seems powerful as anti-aggro tech (and depending on the deck can be a 1-mana cantrip in the late-game).

Rune-Sealed Wall (U): A better Geist of the Archives, but this is really a 3-mana removal spell that slowly gets you card selection. And put that way, I actually like it more. I still think it costs too much and doesn’t do enough, but it’s interesting.

No Interest:

Arcane Epiphany (U): On its face it's slightly-worse Unfathomably Truths, but it has the capability of being an instant-speed Concentrate. But unless you’re in a deck that really wants to hit land drops 6+, I’m not sure this is that much better than Thirst for Discovery.

Bigfin Bouncer (C): A mostly better Deadeye Rig-Hauler, but I think you’d prefer any of the 3-mana Man-o’-War variants or Mist Raven.

Clinquant Skymage (U): Strictly worse Oneirophage.

Delightful Discovery (U): Behold the Multiverse will be more consistent.

Elementalist Adept (C): The lack of 2 toughness means this is unlikely to be able to ambush anything and survive, so it’s either an option for a flash deck to affect the board while holding up interaction or an aggro card. I don’t think it does the first that well and the second is done better by Spellweaver Eternal.

Erudite Wizard (C): Not a ton different than Lat-Nam Adept, but I like Thopter Mechanic more in that space.

Gilded Scuttler (C): I think you’d rather have the higher power of Frost Trickster.

Grappling Kraken (U): By the time you get to 6-mana, it’s not clear you’ll have easy access to additional land drops, so I’m not sure this is better than Tolarian Kraken.

Icewind Elemental (C): Generally worse P/T than Quicksilver Fisher.

Inspiration from Beyond (U): An improvement over Call to Mind.

Starlight Snare (C): Strictly worse than Bitter Chill or Stay Hidden, Stay Silent.

Strix Lookout (C): I think neither the body or ability are worth the cost. Great flavor text, though.

Uncharted Voyage (C): Strictly worse Vanish from Sight.