SC2Mapster

Quote from StragusMapster: Go

Every Damage-type effect has a reduction of damage per point of armor. Most attacks have 1 there, most spells have 0.

Quote from SkeletalHammer: Go

There are four types of damage, melee, ranged, spell, and splash. They are essentially arbitrary, but have filtering effects on certain abilities.
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There is also an armor multiplier on every damage effect, the default is 1 for melee range and splash damage, aka, every point of armor reduces damage by 1. On spells its zero, so every point of armor doesn't do anything. What type of damage does your kerrigan do?

Quote from Kueken531: Go

The amount of damage reduced per armor point is set at each individual damage effect. If you created new damage effects, you probably didn't do that.

They are absolutely correct. I'm starting to have a feeling that you ignore the most important part of what we're trying to tell you.
Go to Kerrigans weapon which pierces armor, select its damage effect and check its "Armor Reduction" field. If it's 0 then damage will ignore armor. If its 1 then each point of armor will subtract 1 point from damage (as already has been stated 3 times). And that really seems to be your issue to be honest :l

Quote from Faust7777: Go

...the marine takes 50 damage every 3 or 4 attacks. At 0 armor, the marine takes 50 damage almost every attack. How is this determined? This makes it very hard to balance.

On another, more annoying note: How can I get Odin to attack Zerglings? I have looked everywhere in the data module and can't find anything that would keep him from doing so.

And these two.. just seems that you did something wrong. And there can be multiple things that you did wrong, so guessing is probably not an option. You probably should either figure it out yourself by comparing your data with original data, or post the map.