Shiny monsters have left an impression to players due to its rarity and its ability to escape with its high speed. Players are used to spending AF bar just to kill the shinies.
However, now we no longer need to do this as there is a way to kill shiny monsters without using AF.
I have tested the following method myself in Forest of Forgetfulness AD, Otherlands Hard and Very Hard, and it works 100%. All shinies are dead, nothing escaped.
To achieve this, you need to:
Have Felmina (Another Style)
in your active party
The reason for this is because Felmina (Another Style) is the only hero with a preemptive stun attack.
Since the attack is preemptive, it allows her to act first even before any fastest hero in your team, and this includes the shiny monster.
In addition, with her stun attack, the shiny monster will be stunned.
Based on my experience killing over 10 shinies this way, the monster is always stunned. Hence, it is a guaranteed kill.
Here is a video showing how I kill them without AFNow, you do not need to hold that AF bar for this monster. Simply have her with the skill in your active party and you are good to go.
Just in case you want to find out any other heroes with preemptive attack, here is the list: Preemptive Heroes
Hope this helps! =)