Imbue reminds me of my own mechanic of the same name. Nice parallel design. Seems a terrible fit for U/R though. Not only are Izzet traditionally an instant and sorcery guild, but a "creatures that want to die" mechanic seems a terrible fit for a guild that's got not black in its identity.

I'd be up for seeing some different takes on R/U than just "instants and sorceries". This at least manages to be more Johnny than both previous Izzet mechanics (a complaint Mark Rosewater made himself about Replicate and Overload).

Hm.. true. But Circeus' 'wants to die' comment does strike me as an odd match for Izzet. I would expect Black, White then Green to have this mechanic, in that order. The colors of Soulshift, incidentally.

With Blue and Red, however, I'd expect the mechanic to look closer to something like this:

­: Imbue. (To imbue, exile this card from your hand targeting a creature you control. That creature gains all abilities of this card.)

It could happen from the battlefield as well, kind of like Tin-Wing Chimera and company. Though, I got to admit, that's got more of a Simic feel to it. I'm not a fan of how what I wrote causes card disadvantage. You could solve that by adding "Draw a card, then imbue" to a number of these.

Alternatively, these cards could exile on death, then you could imbue them whenever you wanted from exile. It makes it feel a little more Blue/Red, but if you do that, I'd suggest imbuing at sorcery speed only. Otherwise, you're breaking NWO rules on combat complexity in common.