Well, I got myself banned on IGN, so here are logs of the new debuff changes using the 50%, 30%, and 15% versions:
These are with a 46 Spirit/28 Body Spec.
[23:07:36] @
@you say, "31% Spirit 25% Body"
(Note - it said 31% Spirit Resist on screen, but 27% in the log.)
[23:07:56] Azurecaeus challenges you to a duel! /duel accept to begin, /duel decline to decline.
[23:08:05] You accept your duel! Begin fighting!
[23:08:31] Your Body resistance has decreased.
[23:08:31] You feel more vulnerable to physical magic!
[23:08:33] You've been in combat recently, the spell has no effect on you!
[23:08:35] Your physical vulnerability fades.
[23:08:35] Your Body resistance increased.
Level 46 Body Debuff - 50% lasted 4 seconds with just 27% Spirit Resist
[23:10:48] Azurecaeus casts a spell!
[23:10:48] Your Body resistance has decreased.
[23:10:48] You feel more vulnerable to physical magic!
[23:10:48] You've been in combat recently, the spell has no effect on you!
[23:10:52] Your physical vulnerability fades.
[23:10:52] Your Body resistance increased.
Level 46 Body Debuff Again - lasts 4 seconds.
[23:11:10] Azurecaeus casts a spell!
[23:11:10] Your Body resistance has decreased.
[23:11:10] You feel more vulnerable to physical magic!
[23:11:11] You've been in combat recently, the spell has no effect on you!
[23:11:13] <Begin Info: Bonuses (snapshot)>
[23:11:13] Resistances
[23:11:13] Crush: +14%/+0%
[23:11:13] Slash: +19%/+0%
[23:11:13] Thrust: +8%/+0%
[23:11:13] Physical: +0%/+0%
[23:11:13] Heat: +0%/+0%
[23:11:13] Cold: +0%/+0%
[23:11:13] Matter: +12%/+0%
[23:11:13] Body: -6%/+0%
[23:11:13] Spirit: +27%/+0%
[23:11:13] Essence: +0%/+0%
[23:11:13] Energy: +16%/+0%
[23:11:13] <End Info>
[23:11:14] Your physical vulnerability fades.
[23:11:14] Your Body resistance increased.
[23:11:22] @
@you say, "-6%"
-6% Now, instead of -32%, and again 4 second duration.
[23:11:49] Azurecaeus casts a spell!
[23:11:49] Your Body resistance has decreased.
[23:11:49] You feel more vulnerable to physical magic!
[23:11:52] Azurecaeus casts a spell!
[23:11:52] You are hit for 357 damage.
[23:11:53] You've been in combat recently, the spell has no effect on you!
[23:11:55] Your physical vulnerability fades.
[23:11:55] Your Body resistance increased.
357 Damage with MoM II using the new Level 50 Lifetap
[23:12:14] Your Body resistance has decreased.
[23:12:14] You feel more vulnerable to physical magic!
[23:12:16] Azurecaeus casts a spell!
[23:12:16] You are hit for 384 damage.
[23:12:20] You've been in combat recently, the spell has no effect on you!
[23:12:21] Azurecaeus casts a spell!
[23:12:21] You resist the effect!
[23:12:21] Your physical vulnerability fades.
[23:12:21] Your Body resistance increased.
Managed to get 2 off this time! Including a 28 point crit, second Level 50 Lifetap resisted, of course.
[23:12:46] Azurecaeus casts a spell!
[23:12:46] Your Body resistance has decreased.
[23:12:46] You feel more vulnerable to physical magic!
[23:12:48] You've been in combat recently, the spell has no effect on you!
[23:12:48] Azurecaeus casts a spell!
[23:12:48] You are hit for 364 damage.
[23:12:56] Your physical vulnerability fades.
[23:12:56] Your Body resistance increased.
[23:12:56] Azurecaeus casts a spell!
[23:12:56] You resist the effect!
[23:12:56] You've been in combat recently, the spell has no effect on you!
Got only 1 Lifetap off again, the next was were after the debuff faded, resisted of course.
[23:13:06] Azurecaeus casts a spell!
[23:13:06] Your Body resistance has decreased.
[23:13:06] You feel more vulnerable to physical magic!
[23:13:06] You've been in combat recently, the spell has no effect on you!
[23:13:09] Azurecaeus casts a spell!
[23:13:09] You are hit for 444 damage.
[23:13:11] Your physical vulnerability fades.
[23:13:11] Your Body resistance increased.
[23:13:15] Azurecaeus casts a spell!
[23:13:15] You are hit for 264 damage.
Another example of the power of Mythic's new debuff. A nice crit on the first one (83) but not enough time to get a second one off. So not only is it a 30% outright damage reduction, but further complicated by the useless nature of the Debuff. If you try to debuff nuke and a single debuff is resisted you will do less damage over time than if you straight out nuked for 270 or whatever.
[23:17:52] Azurecaeus casts a spell!
[23:17:52] Your Body resistance has decreased.
[23:17:52] You feel more vulnerable to physical magic!
[23:17:52] You've been in combat recently, the spell has no effect on you!
[23:17:54] <Begin Info: Bonuses (snapshot)>
[23:17:54] Resistances
[23:17:54] Crush: +14%/+0%
[23:17:54] Slash: +19%/+0%
[23:17:54] Thrust: +8%/+0%
[23:17:54] Physical: +0%/+0%
[23:17:54] Heat: +0%/+0%
[23:17:54] Cold: +0%/+0%
[23:17:54] Matter: +12%/+0%
[23:17:54] Body: +7%/+0%
[23:17:54] Spirit: +27%/+0%
[23:17:54] Essence: +0%/+0%
[23:17:54] Energy: +16%/+0%
[23:17:54] <End Info>
[23:17:56] Your physical vulnerability fades.
[23:17:56] Your Body resistance increased.
[23:17:58] You've been in combat recently, the spell has no effect on you!
[23:18:02] @
@you say, "7%"
30% Debuff, same pathetic duration. A few more examples of the 30% debuff in action:
[23:18:15] Azurecaeus casts a spell!
[23:18:15] Your Body resistance has decreased.
[23:18:15] You feel more vulnerable to physical magic!
[23:18:20] Azurecaeus casts a spell!
[23:18:20] Your Body resistance has decreased.
[23:18:20] You feel more vulnerable to physical magic!
[23:18:22] Azurecaeus casts a spell!
[23:18:22] You are hit for 357 damage.
[23:18:23] You've been in combat recently, the spell has no effect on you!
[23:18:26] Your physical vulnerability fades.
[23:18:26] Your Body resistance increased.
[23:18:31] You've been in combat recently, the spell has no effect on you!
[23:18:31] Azurecaeus casts a spell!
[23:18:31] Your Body resistance has decreased.
[23:18:31] You feel more vulnerable to physical magic!
[23:18:35] Azurecaeus casts a spell!
[23:18:35] You are hit for 345 damage.
[23:18:35] You've been in combat recently, the spell has no effect on you!
[23:18:37] Your physical vulnerability fades.
[23:18:37] Your Body resistance increased.
[23:19:17] Azurecaeus casts a spell!
[23:19:17] Your Body resistance has decreased.
[23:19:17] You feel more vulnerable to physical magic!
[23:19:17] You've been in combat recently, the spell has no effect on you!
[23:19:21] Azurecaeus casts a spell!
[23:19:21] You are hit for 357 damage.
[23:19:22] Your physical vulnerability fades.
[23:19:22] Your Body resistance increased.
[23:19:24] You've been in combat recently, the spell has no effect on you!
his hammer!
[23:19:24] Azurecaeus casts a spell!
[23:19:24] You are hit for 269 damage.
Next are some using the 30% and 15% at 36 Body/38Spirit/11Matter
36(+14) Body 38(+11) spirit 11 matter
[02:34:10] Azurecaeus casts a spell!
[02:34:10] Your Body resistance has decreased.
[02:34:11] You feel more vulnerable to physical magic!
[02:34:13] <Begin Info: Bonuses (snapshot)>
[02:34:13] Resistances
[02:34:13] Crush: +14%/+0%
[02:34:13] Slash: +19%/+0%
[02:34:13] Thrust: +8%/+0%
[02:34:13] Physical: +0%/+0%
[02:34:13] Heat: +0%/+0%
[02:34:13] Cold: +0%/+0%
[02:34:13] Matter: +12%/+0%
[02:34:13] Body: +7%/+0%
[02:34:13] Spirit: +27%/+0%
[02:34:13] Essence: +0%/+0%
[02:34:13] Energy: +16%/+0%
[02:34:13] <End Info>
[02:34:16] Your physical vulnerability fades.
[02:34:16] Your Body resistance increased.
The 30% debuff actually debuffed him from 25 to 7 Body resist or 18%. It lasted for 5 seconds this time, although my guess is it was actually just a tad over 4 since we do not see fractions of a second.
[02:34:30] Azurecaeus casts a spell!
[02:34:30] Your Body resistance has decreased.
[02:34:30] You feel more vulnerable to physical magic!
[02:34:33] <Begin Info: Bonuses (snapshot)>
[02:34:33] Resistances
[02:34:33] Crush: +14%/+0%
[02:34:33] Slash: +19%/+0%
[02:34:33] Thrust: +8%/+0%
[02:34:33] Physical: +0%/+0%
[02:34:33] Heat: +0%/+0%
[02:34:33] Cold: +0%/+0%
[02:34:33] Matter: +12%/+0%
[02:34:33] Body: -8%/+0%
[02:34:33] Spirit: +27%/+0%
[02:34:33] Essence: +0%/+0%
[02:34:33] Energy: +16%/+0%
[02:34:33] <End Info>
[02:34:36] Your physical vulnerability fades.
[02:34:36] Your Body resistance increased.
[02:34:45] Your character has been saved.
[02:35:09] @
@you say, "Critted Debuff for 26"
Interesting, Wild Arcana II still allows for critical debuffs. Notice that once again it lasted almost 6 seconds. This is odd, they were lasting barely 4 earlier.
[02:35:21] Azurecaeus casts a spell!
[02:35:21] Your Body resistance has decreased.
[02:35:21] You feel more vulnerable to physical magic!
[02:35:26] <Begin Info: Bonuses (snapshot)>
[02:35:26] Resistances
[02:35:26] Crush: +14%/+0%
[02:35:26] Slash: +19%/+0%
[02:35:26] Thrust: +8%/+0%
[02:35:26] Physical: +0%/+0%
[02:35:26] Heat: +0%/+0%
[02:35:26] Cold: +0%/+0%
[02:35:26] Matter: +12%/+0%
[02:35:26] Body: +7%/+0%
[02:35:26] Spirit: +27%/+0%
[02:35:26] Essence: +0%/+0%
[02:35:26] Energy: +16%/+0%
[02:35:26] <End Info>
[02:35:27] Your physical vulnerability fades.
[02:35:27] Your Body resistance increased.
Same thing again.
[02:35:43] Azurecaeus casts a spell!
[02:35:43] Your Body resistance has decreased.
[02:35:43] You feel more vulnerable to physical magic!
[02:35:45] Azurecaeus casts a spell!
[02:35:45] You resist the effect!
[02:35:47] Azurecaeus casts a spell!
[02:35:47] You are hit for 360 damage.
[02:35:49] Your physical vulnerability fades.
[02:35:49] Your Body resistance increased.
[02:35:49] Azurecaeus casts a spell!
[02:35:49] You resist the effect!
[02:35:53] Azurecaeus casts a spell!
[02:35:53] You are hit for 324 damage.
[02:35:53] Azurecaeus casts a spell!
[02:35:53] You are hit for 290 damage.
[02:35:53] Your duel ends!
360 Hit is a crit for 33. So Full Body spec nuke during the debuff time frame is around 325 with MoM II and a 30$ Body debuff.
[02:36:47] Azurecaeus casts a spell!
[02:36:47] Your Body resistance has decreased.
[02:36:47] You feel more vulnerable to physical magic!
[02:36:47] Azurecaeus casts a spell!
[02:36:47] You are hit for 363 damage.
[02:36:51] Azurecaeus casts a spell!
[02:36:51] You are hit for 363 damage.
[02:36:51] Your physical vulnerability fades.
[02:36:51] Your Body resistance increased.
This time it only lasted 4 seconds again. Maybe it is variance from no longer being full Spirit Spec.
[02:37:34] Azurecaeus casts a spell!
[02:37:50] You are hit for 292 damage.
[02:37:53] You are hit for 359 damage.
[02:37:54] You are hit for 290 damage.
[02:37:54] Your duel ends!
3 non-debuffed nukes with one crit for 70. Performs just as well as the debuffed nukes if not better.
[02:38:53] @
@you say, "trying 15% Debuff"
[02:39:08] Azurecaeus accepts the duel. Begin fighting!
[02:39:28] Your Body resistance has decreased.
[02:39:28] You feel more vulnerable to physical magic!
[02:39:30] Your Body resistance has decreased.
[02:39:30] You feel more vulnerable to physical magic!
[02:39:32] <Begin Info: Bonuses (snapshot)>
[02:39:32] Resistances
[02:39:32] Crush: +14%/+0%
[02:39:32] Slash: +19%/+0%
[02:39:32] Thrust: +8%/+0%
[02:39:32] Physical: +0%/+0%
[02:39:32] Heat: +0%/+0%
[02:39:32] Cold: +0%/+0%
[02:39:32] Matter: +12%/+0%
[02:39:32] Body: +8%/+0%
[02:39:32] Spirit: +27%/+0%
[02:39:32] Essence: +0%/+0%
[02:39:32] Energy: +16%/+0%
[02:39:36] Your physical vulnerability fades.
[02:39:36] Your Body resistance increased.
[02:40:02] @
@you say, "14 Point Crit - 8% Body"
A critted 15% Body debuff takes him from 25% to 8%.
[02:40:11] You resist the effect!
[02:40:12] You resist the effect!
[02:40:24] Your Body resistance has decreased.
[02:40:24] You feel more vulnerable to physical magic!
[02:40:28] <Begin Info: Bonuses (snapshot)>
[02:40:28] Resistances
[02:40:28] Crush: +14%/+0%
[02:40:28] Slash: +19%/+0%
[02:40:28] Thrust: +8%/+0%
[02:40:28] Physical: +0%/+0%
[02:40:28] Heat: +0%/+0%
[02:40:28] Cold: +0%/+0%
[02:40:28] Matter: +12%/+0%
[02:40:28] Body: +16%/+0%
[02:40:28] Spirit: +27%/+0%
[02:40:28] Essence: +0%/+0%
[02:40:28] Energy: +16%/+0%
[02:40:28] <End Info>
[02:40:29] Your physical vulnerability fades.
[02:40:29] Your Body resistance increased.
[02:40:36] @
@you say, "No crit - 16% Body"
[02:40:49] Your Body resistance has decreased.
[02:40:49] You feel more vulnerable to physical magic!
[02:40:50] You are hit for 360 damage.
[02:40:54] You are hit for 328 damage.
[02:40:54] Your physical vulnerability fades.
[02:40:54] Your Body resistance increased.
More variance on the duration of the debuff (30% Debuff here), this time 5 seconds. I am not sure what is causing that.