Assassination and Drain Skill? (Yanfly Skill Core)

[Scoodles]

Hello, everyone.


Currently trying to implement a skill similar to the 'Climax' Skill from Etrian Odyssey. The ability goes as such:

• The user attacks the enemy.
  
• If the Target is below a certain HP limit (In this case, 40%), the attack hits.
  
• Otherwise, the attack completely misses.
  
• If the attack hits, there's a chance the ability instantly kills the Target.
  
• The User then drains for a quarter of the damage dealt.
  

I'd like to implement the ability into a game I'm working on just with a bit of changes.

• Rather than the attack miss outright, the ability just does regular damage.
  
• If the ability is used on a boss like Monster under the threshold (Determined by probably a variable or switch that's turned on before the battle), it forces a critical instead.
  

I'd appreciate the help for this, if possible.