EDIT: After some feedback I am going to try the Massive Damage optional rule in the DMG and see if that takes care of my goal. The OP is below for people who still care to chime in.There's an idea I've been toying with and I'm interested in some back and forth on it.
When you hit on an attack and your total attack roll is 10 or more than the target's AC, you deal double damage. If you hit by 15 or more, your damage is tripled. You do not roll additional dice, you simply multiple your base damage by the bonus multiple.
Ex. Behgord the Barbarian has a +9 attack bonus and is attacking an Ogre with AC 11. The player rolls a 17, for a total of 26. Since this is exactly 15 higher than the Ogre's AC, when the player rolls damage of 11 for Behgord, the damage is mulitplied by 3 to 33 points.
Later, Behgord is fighting an orc guard with AC 15. The player rolls another 17! Since the total is 26, which is 11 higher than the AC 15, the damage is doubled. When Behgord's player rolls 9 damage, it is doubled to 18 and the orc (only 15 hp) is killed.
If your attack resulted in a critical hit, you roll double dice for critical damage and then multiply it.
Now, what am I trying to accomplish with this idea?
I am looking for something so higher level characters can more easily defeat mooks with a good single hit. Think of something like LotR movies. Aragorn, Gimli, and Legolas all routinely defeat goblins and orcs with single strikes, but in 5E this is not easily represented as far as I see.
Saves failed by 10 or more could also result in higher damage, longer durations, etc.
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ASIDE:
FYI, my original idea was this:
If you hit on an attack, you make another attack roll. If you succeed, you roll again, and so on until you miss. For each "hit", you multiply your rolled damage. If the first attack was a critical, you double the dice and then multiply for an additional "hits."
Ex. Behgord only needs a 2 to hit the ogre, so will likely hit, and hit several times over before rolling a 1. If the total rolls that hit were, say 7, his damage if he rolled 11 would be 77, killing the ogre.
Now, this was TOO much by far, so I came up with the other version of 10-over and 15-over hits.
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Thoughts? While I like the idea, I am not certain at all of the execution of it...
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