This is from a yanfly's Tips and tricks video, you can find it here:
I've changed it a bit so it only deals Hp damage, the formula in
Red means how much damage will the target receive for each debuff. This edit changes these things from yanfly's original idea so it fits your request:
-It shouldn't check for buffs (tho I'm not sure 100%, try it and you tell me

)
- I deals damage for each debuff.
-It shoulnd't remove or clear them
You'll need these plugins to make it work:
Battle engine core:
http://yanfly.moe/2015/10/10/yep-3-battle-engine-core/
Skill core:
http://yanfly.moe/2015/10/13/yep-8-skill-core/
My last suggestion is you should have the skill deal at least 1 damage or debuff the target, because the damage from the formulas below will occur after the skill's formula box happens. Anyways, test it if you want and you tell me. It should work and do what you wanted, but in case it doesn't, as I can't test it now, write me and I'll fix it, I'm pretty sure I can make it work

.
<After Eval>
// Initialize the HP value.
var hp = 0;
// Loop through all 8 parameters.
for (var i = 0; i < 8; i++) {
// If it is a debuff...
if (target._buffs
< 0) {
// Then increase the damage by a formula.
hp -= user.mdf * 2;
}
// Check if the HP change is negative...
} if (hp < 0) {
// Play an animation.
target.startAnimation(animation Id from your animations list here);
}
// Check if the HP amount isn't 0...
if (hp !== 0) {
// Alter the target's HP.
target.gainHp(hp);
// Start the damage popup for the target.
target.startDamagePopup();
}
// Clear the target's results.
target.clearResult();
</After Eval>