Someone

    public boolean calcBlueSkillSuccess(L2Character activeChar, L2Character target, L2Skill skill)
    {
        int atk = activeChar.getPAtk(activeChar);
        int def = 0;
        int modifier = 0;
        int rate = 0;
        int rateMin = _rnd.nextInt(100);
        switch (skill.getSkillType()) {
            case STUN:
                def = target.getMDef(target, skill);
                modifier = target.getWIT();
                break;
            case ROOT:
                def = target.getMDef(target, skill);
                modifier = target.getDEX();
                break;
            case PARALYZE:
                def = target.getPDef(target);
                modifier = target.getWIT();
                break;
            case SLEEP:
                def = target.getMDef(target, skill);
                modifier = target.getWIT();
                break;
            default:
                def = target.getPDef(target);
                modifier = target.getCON();
                break;
        }
        def = _rnd.nextInt(modifier) * (def / modifier);
        rate = (atk - def) / (atk + def);

        if (rate > 100) rate = 100;         // We shouldn't have more than 100% success rate
        if (rate < 1) rate = 1;             // We shouldn't have less than 1% success rate

        return (rateMin <= rate);
    }