Most of the skill's damage come from the cast cost, though.
https://github.com/rathena/rathena/blob/master/db/pre-re/skill_require_db.txt
// SkillID,HPCost,MaxHPTrigger,SPCost,HPRateCost,[...]
254,0,0,37:44:51:58:65:72:79:86:93:100,20,0,0,99,0,0,none,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 //CR_GRANDCROSS