One interesting point is timimg. It is very possible that the victim will get to attack before the crows that surround it do so. I.e. the victim may get to attack before the crows kill it.
Also important. Suppose that a crow ends up placed in between two creatures, e.g. its target and a creature 2 spaces away.
Does the crow only attack its target or does it attack its target as well as the other adjoining creature?
Lastly, what happens if a crow is lobotomized? Will it turn into a regular creature?
What about with spells like overdrive or liquid shadow? Will the crow still attack its target or will the new abilities overwrite this effect?
I think this card can be quite potent as a CC measure, but I don't think it will end up OP (no matter what you decide on the above points). The reason being that there is significant lag time between when this is cast and when the CC takes place. This leaves an entire turn for your opponent to deal with the potential CC threat.
Moreover, if lobo'd crows become normal creatures, this spell could end up backfiring on you.
E.g. SoPa + lobo...
lastly, the potency of this CC is very much correlated with the density of your opponents field. It is usesless against a full field and will have little effect against targets that already have several ally creatures nearby.
I think this is a very creative and interesting card. I'ld love to test it out in Cygnia some day if it makes it there.
P.S. What do you think about using "Murder of Crows" as the name instead? It sounds much more descriptive and gives a nice sinister CC feel to the theme