did this guy test well for you or are you speaking hypothetically? because he was pretty awful when i played him. i had a very exciting deck with multiple tutors that ensured i got him flipped when necessary but the majority of the time i was cutting him because a tempo-focused blue has too many creatures to ensure he flips regularly. i think he might be better in a more traditional blue section with mostly spells, but that section is a lot less interested in running him.
I tested Delver for a bit. I actually really like him, but as you say, he's much more inconsistent than in constructed. I was playing with the idea of overhauling my blue section, getting rid of some of the more expensive control-only cards like Dismiss etc, and going with a more tempo/disruption/aggressive feel. Delver could certainly come back in that environment.
What are the core (and fringe I suppose) cards to support U Tempo in a cube?
Mono-blue tempo decks are likely to be rubbish, whatever you add to your cube. You could likely create some nice two colour tempo decks with blue in them though.
I tested Delver for a bit. I actually really like him, but as you say, he's much more inconsistent than in constructed. I was playing with the idea of overhauling my blue section, getting rid of some of the more expensive control-only cards like Dismiss etc, and going with a more tempo/disruption/aggressive feel. Delver could certainly come back in that environment.
Juju Alters - Altered MTG Cards
Mono-blue tempo decks are likely to be rubbish, whatever you add to your cube. You could likely create some nice two colour tempo decks with blue in them though.
I'm a fan of:
Azorious Guildmage
Opposition
Tradewind Rider
Delver of Secrets
Remand
Memory Lapse
Into the Roil
Snapcaster Mage
Not to mention all of the Man-o'-War like dudes like Venser, Shaper Savant, Aether Adept, Riftwing Cloudskate, and even the new 2UU one from Avacyn Restored.
One card that I always liked the look of was Annex. Seems like a mono blue Mwonvuli Acid-Moss
Juju Alters - Altered MTG Cards