heal atks "zombie" monsters.
list:
ZOMBIE mushroom
ZOMBIE lupins
coolie ZOMBIE
minor ZOMBIE
and wraiths/jr. wraiths.
Usually, HS does tell you if the monster is weak to HEAL, which is different than HOLY. HOLY refers to light atks in general (so now "holy arrow"). weak to HEAL is just the atk "heal".
And, lightning mages shouldn't train at zombies cause it cost a lot of pots. they do plenty of dmg to u, while clerics heal and they don't need hp pots.
Damage wise: Lightning does 60 spell dmg to every monster it atks. Thats a total of upto 360 spell dmg. Clerics heal does mor than 60 spell dmg to ONE or TWO creatures, but it decreases against more creatures. Lightning hits consistently against 6 monsters, but heal will do less (to each) if there are 6 monsters.
In thrid job, although ice strike 90 spell dmg is less than 105 shining ray, ice mages hav element affinity which increase speel dmg by 135%, soooooo, its mor than 105.
In the end, Ice/lightning will do more dmg, but, as said before, clerics' skills like doom, holy symbol, dispel, and mystic door all make it a VERY worth class. Then again, if ur going for dmg, u should choose fire anyway b/c it has 120 mass strike in 3rd job XP