I have thought of this idea months ago and to an extent...
Moogle devised to me a way to make a new battle system where zlings were under your character to make a blood effect and subtract points from custom score to make hp trigger based.
I rotated this many ways and found out only neutral units would work as regular cpu or human burrowed units unburrowed which was a REAL problem. If you are gonna use neutral units, you also need to give each player a different burrowed unit under him so that burrowed units won't switch around randomly.
I thought this idea was bad because 1) you needed to waste a burrowed zerg unit on each player playing, 2) a player slot is wasted on neutral and 3) the harder enemies will depend more on their attack rate rather than damage.
Although I could bypass problem 3 by giving each burrowed unit more hp, I still found it not suitable to my likings. Therefore I was in deep discussion with some others one day and an idea came to my head... use... LURKERS!
Yes, it maybe unconfortable to some people seeing a lurker underneath your player, but it truly is a new way to do things and did I mention so flexible? You can modify the lurkers hp to your likings (I choose 100hp) and when it dies, create another lurker and subtract custom score from your total.
This system allows modifiable potions and hp regeneration. Not only that, but you can add randomized triggers to do the "affects" you were discussing where some attacks do 200%, 100% or even 0% damage to the player. I have included a map that you may find interesting.
I tried another way of doing this "randomized" damage. When your hero dies, it gets respawned and you lose a percentage of custom score. The problem is, it maybe hard to get your hero out of the battle when he is getting hit because you can't move him when he is dead or the moment when he respawns.
So check this map out and maybe it maybe give you ideas. Ezday2 helped me formulate some ideas as well. I lost the original and it's protected so...