mobs healing enderdragon

Hello, i would like to make some mobs healing the enderdragon, that spawn with spawner, to make the enderdragon fight a bit more complicated

but i dont manage to make the mobs target the enderdragon, it works only if the dragon hit them and then they will use the heal on him. The problem is that the dragon will kill them...

i would like to have static mob, disguised in end crystal (i will do that after), using some heal skill on dragon

here is what zDrakon start to do for me...

mobs healing enderdragon