
Savage defense has finally made it to the PTR. I got to test it a little bit tonight. Nothing insane, but at least stuff that lets us do some basic theorycrafting about it.
It's learnable at the trainer. It requires no talent points.
It has no internal cooldown that I could find. It would proc on any crit, and it would proc after pretty much every swipe on large enough pulls.
It has a 10-second uptime (or until it's used).
SD procs after you already have an SD will refresh the timer, but will not stack. Or, basically, the new proc overwrites the old one. (This is important for later stuff)

And yeah, the buff icon looks unlike the actual skill icon, and looks like
frenzied regeneration.
The graphic and animation is that you stand up and get a little reddish bubble in the middle of you. SD looks a lot like an enrage effect in that respect, and it's very easy to miss the bubble. The bubble is basically entirely contained inside of you. I think. In any case, it's not a big graphic, and you're not running around in a super simian sphere.
It does not proc on DoT effects when they crit.It does proc on the application of DoTs, however - like the first attack of lacerate.
It does not proc on faerie fire.
It does appear to have similar issues to spell reflect, in that multiple attacks can be absorbed by one shield if they happen close enough to each other:
01:48'05.625 Feltest gains 3 Rage from Natural Reaction.
01:48'05.625 Feltest gains Savage Defense.
01:48'05.625 Feltest's Savage Defense is refreshed.
01:48'05.641 Feltest's Savage Defense is refreshed.
01:48'05.641 Feltest's Savage Defense is refreshed.
01:48'05.641 Feltest gains Reflection of Torment.
01:48'05.641 Feltest's Savage Defense is refreshed.
01:48'05.641 Feltest gains 3 Rage from Natural Reaction.
01:48'05.672 Demon Hunter Supplicant #79 attack was absorbed by Feltest. 01:48'05.672 Demon Hunter Supplicant #59 attack was absorbed by Feltest.The big one for me:
it is heavily affected by latency, as far as I can tell, and still has significant bugs. Not that that's a surprise, but keep them in mind. I'd often see a SD proc happen a second or so after actually critting a mob - even after the LotP proc that would trigger. In my testing above, I also came across parts where the log said I'd gain SD but the shield would not absorb anything. I think this is due to it breaking when facing significant amounts of mobs (I was pulling supplicants at BT as a test). Here's an example:
01:48'02.812 Feltest gains 3 Rage from Natural Reaction.
01:48'02.812 Feltest Swipe hits Demon Hunter Supplicant #56 for 911 Physical. (Critical)
01:48'02.812 Feltest Swipe hits Demon Hunter Supplicant #68 for 911 Physical. (Critical)
01:48'02.828 Feltest Swipe hits Demon Hunter Supplicant #60 for 442 Physical.
01:48'02.844 Feltest Swipe hits Netharel #2 for 443 Physical.
01:48'02.844 Feltest Swipe hits Demon Hunter Supplicant #59 for 911 Physical. (Critical)
01:48'02.844 Feltest Swipe hits Demon Hunter Supplicant #58 for 911 Physical. (Critical)
01:48'02.844 Feltest Swipe hits Demon Hunter Supplicant #69 for 442 Physical.
01:48'02.844 Feltest Swipe hits Demon Hunter Supplicant #66 for 442 Physical.
01:48'02.844 Feltest Swipe hits Demon Hunter Supplicant #70 for 443 Physical.
(at this point, I should receive a SD proc)01:48'02.875 Demon Hunter Supplicant #70 melee swing hits Feltest for 72 Physical.
(and naturally I don't, and get hit anyway)01:48'02.922 Demon Hunter Supplicant #79 attack was dodged by Feltest.
01:48'03.172 Demon Hunter Supplicant #66 attack was dodged by Feltest.
01:48'03.187 Netharel #2 attack was dodged by Feltest.
01:48'03.187 Netharel #2 attack was dodged by Feltest.
01:48'03.203 Demon Hunter Supplicant #68 died.
01:48'03.203 Demon Hunter Supplicant #60 died.
01:48'03.203 Demon Hunter Supplicant #58 died.
01:48'03.203 Feltest gains 3 Rage from Natural Reaction.
01:48'03.203 Feltest gains Savage Defense.
01:48'03.219 Feltest's Savage Defense is refreshed.
01:48'03.219 Feltest's Savage Defense is refreshed.
01:48'03.219 Feltest's Savage Defense is refreshed.
(now I gain the SD proc - and it's refreshed multiple times. Presumably because I got a total of 4 crits, and each crit separately can make an SD proc - and they all overwrite each other).01:48'03.250 Demon Hunter Supplicant #55 attack was dodged by Feltest.
01:48'03.250 Demon Hunter Supplicant #55 attack misses Feltest.
01:48'03.578 Feltest melee swing hits Demon Hunter Supplicant #55 for 825 Physical.
01:48'03.578 Demon Hunter Supplicant #70 attack was dodged by Feltest.
01:48'03.609 Demon Hunter Supplicant #66 gains Evasion.
01:48'03.609 Feltest gains 5 Rage from Primal Fury.
01:48'03.625 Feltest gains 5 Rage from Primal Fury.
01:48'03.625 Feltest gains 5 Rage from Primal Fury.
01:48'03.625 Feltest gains 5 Rage from Primal Fury.
01:48'03.625 Feltest gains 3 Rage from Natural Reaction.
01:48'03.625 Feltest gains 3 Rage from Natural Reaction.
01:48'03.625 Feltest gains 3 Rage from Natural Reaction.
01:48'03.625 Feltest gains 3 Rage from Natural Reaction.
01:48'03.656 Demon Hunter Supplicant #79 melee swing hits Feltest for 81 Physical.
(
this is where I should have used the shield. I did not).01:48'03.656 Demon Hunter Supplicant #59 attack misses Feltest.
01:48'03.656 Demon Hunter Supplicant #69 attack misses Feltest.
01:48'03.875 Demon Hunter Supplicant #80 attack misses Feltest.
More testing is required, of course, but my suspicion is that the multiple 'refreshes' confuses the system and causes you to effectively lose your shield. I also think it's somewhat flawed that the shield happens so long (relatively speaking) after the actual event; it means that if you happen to crit in between the first crit and the shield proc, you will just overwrite the shield instead of having it used on any attacks in the meantime. Is that problematic in practice? Not exactly. But it makes it less effective than it should be.
The tooltip is interesting, in that it implies that the shield's absorption is not tied to your AP at the time you spawned it - only at the time that you get hit. Not sure why this would ever matter, but I plan on testing it at some point.
Things I'll be testing:
whether or not it does absorb 25% of your AP (only tested against weak mobs tonight)
whether a DoT tick or something else like it (reflective damage, for example) will remove the shield
If the absorption is based on AP at the time of proc or at the time of use
further testing to see if I can narrow down when you get a shield or not (the bug above)
Any requests for testing that you'd like to see? I'm limited in time and what gear I have, but I'll try my best to oblige.