Two notes:

Shouldn't this card have flying? Most illsuions fly...

I can't resist suggesting a line like ": Target illusion."

I gave it flying which does indeed make sense.
Was thinking of a card somewhat like this: Grounded in Reality Target Illusion loses flying and isn't an Illusion until end of turn.
Very specific though so maybe "target creature loses flying and the Illusion subtype UEoT" would be better. For the blue on blue matches

": Target illusion." is absolutely hilarious. I reluctantly concede it probably shouldn't be printed, but it's cool :) For that matter, it could say "Target illusion gets +3/+3 and gains flying UEOT" and it would be funny :)

heh why not go all out - target illusion gets +0/+0 UEoT - it does nothing to illusions without the target sac clause but for those that do......
Better yet make him Rare and add "All Illusions have 'when this becomes the target of a spell or ability sacrifice it.'" for lots of funky fun.
For even more fun combo it with Field of Dreams from the Multiverse Design Challenge

I was originally trying to think of a funny creature type that the illusions could turn into to indicate that they are now dead. Something like "T: Target Illusion becomes Mist". Unfortunately, neither Elemental or Golem get the idea across, and Shade was too abstract a joke.

LOL. I like "+0/+0" :)