GilVallus
Green Slime
It's somewhat rare and seems to correspond with taking damage (or something), but sometimes using the skill will cause a graphical glitch for a split second around a character. It's very brief, so capturing the glitch in the act is tricky. Either the attack is pulling a blown-up, broken version of the player sprite or from random assets, either way I haven't had it happen recently enough to know for sure exactly what kind of square specter is manifesting.