In src/main/java/net/sf/gameserver/model/actor/stat/CharStat.java

This:

    public int getMAtk(L2Character target, L2Skill skill)
    {
        // Get the base MAtk of the L2Character
        double attack = getActiveChar().getTemplate().baseMAtk;
        
        //+50 matk bonus for players having 80 level
        if(getActiveChar().getLevel() == 80) {
            attack += 50;
        }