Critical Strike Stacking

How does this work? I know they stack somehow, but have no idea how.

For example: I have two CS skills on one hero - 1st is quite common crit ( 40% to do 2.5x damage) and second is called Lethal Strike and has much more brutal effect - 15% to do 10x damage. Which would be execuded if both got triggered at once?

I don't actually know very well, but I guess you'll have a unit with 55% chance to do a critical strike, the critical strike has 15% chance to be a 10x one and 40% to be a 2.5x one, and if I'm not wrong, there's a chance that both of them will trigger at the same time, if so, you'll have a critical for 10x plus a critical for 2.5x...
dunno if you understood it, but anyway, can't think of another way to explain it...

It would be great if they stacked this way. I thought one will override the other when triggered at once.

They both trigger independently. If the two occur at once, only the last critical strike skill or item you got will have effect. Skills are only counted as achieved when they are learnt for the first time.

That doesn't explain why you see two different numbers overlapping eachother when a double crit procs.

Unless it renders one null, which I'm not entirely sure it would.

For things like Hardened skin, you're right without a doubt.
...but things like Crit and evasion (highest evasion overrides, I hear), it might be different.

You calculate chances very simply, take this for example.

The chance of getting at least one crit of a 20% chance and a 30% chance are
0.2*0.7 + 0.3*0.8 +0.2*0.3 = 44%

The chance of getting exactly one crit is
0.2*0.7 + 0.3*0.8 = 38%

And the chance of getting the double is
0.2*0.3 = 6%

As for the damage two crits do, I'd say each does it's own damage, and if they both proc, then they both do their respective damage.

In Elemental RPG, it's possible to get 5 sources of Critical Strike(2x, 3x, 4.5x, 5x, 12x), when they simultaneously trigger, you can deal say... 900 damage and 1350 damage. It doesn't seem to do a bazillion damage, rather just a group of smaller strikes.

That's how I saw it in Elemental RPG anyway.

Ok, thanks for explanation

Well I guess it can be changed somewhere because I just tested it again.

You create a peon with 0 armor and 1000HP with no attack.
You modify an hero so he has 100% chance to do 2x damage as an ability and always does that same amount of damage, let's say 50.
You give him an item that gives 100% to do 4x the damages.

If you attack with only the item, you will hit the peon for 200 damages, everytime. You then learn the ability, which override the item, you now hit for 100. Both crit now show but only the 2x is done. You drop the item and pick it up again, you now crit for 200, both crit are shown.

That the basic behaviour, beside removing the melee initialization and creating two forces so the hero will attack the peon, it was a stock map. Now, if anyone know how to make the crit stack and/or how to remove the double crit message, I'm sure a lot of ppl would be interested in knowing how.

use a multi-level ability for each *x damage multiplyer with the chance to crit modifyed on each level. change the level of the ability when a unit gaisn a crit item / skill.

I'm pretty sure that if you want to do anything fancy like combining critical strikes or changing the number display, you would need JASS. Either that, or some very complex triggering.

Oh, and yeah, PsychoPif is correct. Critical strikes do not combine when they both occur. One overrides (I believe the most recently acquired overrides, like he said.) They can still occur independently.