Option 1 is not universal, and probably is not what I wanted.
I would take option 2.
The Idea is, I would like a chance to stun MVPs on each attack instances, when MVP has 50% hp or lower. (2 second stun, based on missing HP %. (stun boss at (100 - ((100 - (remaining hp/maxhp) *100)))) / 10 percentage.)
(I am trying to create an OnPCAttack based on this
http://www.eathena.ws/board/index.php?showtopic=205005)
and probably, is trying to get even closer to my main idea.
(My MVP Battle system is finished except for this feature.., It is a lot different than normal RO, and this feature is absolutely needed.)