Matt will probably post his lil tutor here again xD but ill just explain fast
first way: use the 'special effect' triggers, u can just create special effects on units and remove em to
second way: make a sphere based ability with 0 cooldown and ur targets and attachment points (look at blood mage, he uses it to)
attachments:
foot, left, right
hand, left, right
weapon (for heroes)
chest, left, right
origin (mostly on feet like auras)
overhead (doesnt rotate with head)
head (rotates together with head)
sprite first, second, third (for buildings and blood mage)
and there r more, but not interesting (like mount, rear, and more sprites etc)