The way it stands now, I don't like this card...
First off: As moomoose repeatedly emphasized, the damage swarm mechanic must be employed with care. Its just too powerful when used with mitosis and fractal
Second off: This card's cloak violates both of cloak's innate balancing mechanisms. It has no duration limit. It is invisible itself, meaning there is no way to stop it without resorting to mass CC. This strongly outweighs its limited area of effect. Particularly when used with mitosis or fractal.
That said, it has very good potential.
Here's my 2
on how to balance it:
1) Change it so that it cannot be cloaked itself (e.g. add in "unaffected by cloak")
2) Make it stackable and allow player to choose which slot it plays to.
E.g.: "Stackable: Increases attack
Plays to a target ally field slot.
Cloak field: Cloaks the area its in. Cannot itself be cloaked."
These modifications are designed to force strategic thinking over brute force spamming. Particularly when used with mitosis or fractal combos.
The stacking mechanism can scale non-linearly to provide the swarm like effect of increasing damage but without the added effect of making CC harder at the same time (thereby helping to keep it balanced).
For instance, if you set its attack to scale as N^2 (where N is stack size) you will recover your swarm mechanics damage scaling wrt. number played with the caveat that all must be played to the same stack (making it vulnerable to single target CC).
Being able to choose where to play this card on the field forces you to choose between extending cloak area and increasing total damage done. This will help foster strategy over brute force usage.
A final note: To prevent quintescence abuse, immaterial should prevent further stacking. Of course, a player could still stack first then quint, but it would be a 1 shot deal.