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What's effective armor class in creature modding


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I'm trying to make the enemies in BG 1 tuffer.

Using Near Infinity for creature editing there is a line:

Effective AC

What's this? how does it work with equiped armor?

I've been searching the internet for some hours now without success.

I hope someone here can help me. :laugh:

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I believe (though the more technically knowledgeable may be able to correct me on this), that Effective AC is the actual AC used to determine how hard they are to hit. This allows the developer/modder to make a creature harder or easier to hit, regardless of what armour the creature is wearing, or what it's stats or abilities would normally give it. This should be one of the things you are looking for to make opponents tougher.

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I've done some testing and if anyone is interested this is what I did. I made the experiments with the ogrillon that carries the letter to Mirianne in Beregost


His natural and effective AC values are 6 and 6. His dexterity is 9 and that value doesn't modify his AC. My guy's THAC0 is 5 while equipped with a simple morningstar.


I killed the ogrillon three times without changing anything. That took 11, 10 and 13 swings with the morningstar.


Then I gave him an armor that set the base AC to -10 and killed him three times. This time that took 35, 22 and 44 swings.


In the next test I changed that armor to one that gave a bonus to AC with 10. It now took 21, 25 and 17 swings to kill him.


Finaly I removed the armor and changed the effective AC value to -10. The results was 68, 28 and 70 swings


I know that the number of times i killed the ogrillon in my tests isn't enough to get statistically accurate results but it seems obvious to me that the effective AC value does not override equipped armor.


I belive that if you have a creture with an effective AC of lets say 5 equipped with a full plate mail that sets the AC to 1 and you change the effective value to 2 that change will have no effect.


If anyone disagree please tell me.

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'Number of times I must swing to kill' is pretty useless as a statistic. Options -> Gameplay -> Feedback -> enable 'To Hit Rolls'. This way you can see the rolls 'behind the scene' and figure out that, say, you need a roll of 14 to hit in a case, or a roll of 8 in another, making case #1 harder.

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I've re-done the testing av the effective AC parameter and for what it's worth I just thought I should present my findings.


I used the same ogrillon as before, the one with Mirianne's letter but this time I checked the attack rolls instead of counting swings.


I attacked the ogrillon while his natural and effectiv AC was set to 6 and without armor. It took a roll of 2 to hit him.

Then I gave him an armor that added a bonus of 10 to his AC. It now took a roll of 9 to get a hit. Thus the armor added to the effective AC setting.

The 10 AC bonus should have set his AC to -4 so I made a check with setting the effective AC to -4 and removing the armor. As expected it took a roll of 9 to hit him.


I repeated these tests with an armor that set the ogrillons AC to -10 instead of adding a bonus. With his effective AC set to 6 an attack roll of 15 was required and without the armor but effective AC set to -10 the roll was the same.


Setting the natural or base AC to -10 and the effective to 6 gave the same result as with both natural and effective set to 6. That means the effective AC parameter overrides the natural or base AC parameter.


My conclusion is that the effective AC value does not override the effects of equipped armor. In order to make a creture harder to hit it isn't enough to lower the effective AC value. It is also necessary to check what armor the creature is wearing.


It's a pity, I hoped lowering the effective value would be enough. This means more work for me. As long as their equippes items adds a bonus to AC it's fine to just lower the effective AC value but as soon as they are equipped with an item that sets the base AC I'll have to watch out.

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