Here's a fun one. Phase out effects cancel all commands given to the target, as well as all commands given to units attacking that target. This means you can't target particular units against Vasari, including AI, without reissuing the order every 5 seconds when they activate their ability to phase out and heal. You also can't flee from Vasari without needing to reissue the retreat command or your ships will turn about and start fighting again whenever they get hit by the phase out stun ability the Vasari use.

Quite simply, you cannot fight Vasari without such overwhelming firepower to win without any micro or ever needing to retreat, unless you babysit your fleet throughout the entire fight to the point of being unable to do anything else.