Searing Aura provides 20% concealment. Harssaf deals half fire damage to immune creatures, up to maximum equal to HD.
Ok, first Initiative round: Move in front of the Pit Fiend and leave Sand Form as a swift action.
Standard action: Activate Haste, 15 rounds
Searing Aura damage 1 2d6 : 1, 6, total 7 (halved: 3) (http://minmaxforum.com/index.php?topic=16230.msg335251#msg335251)
With White Raven Tactics, a second round:
Full-attack (Dice roller thread rolls didn't include the +2 from flanking with Dyson, so all rolls below are increased by 2. Each successful crit also increases attack and damage by +1 on subsequent rolls. If at least two attacks hit, the Pit Fiend also must make a Fort save (DC 29, +1 per additional hit) with a +5 bonus or be staggered for 1 round; Additionally, the four main-hand attacks force a Fort save at DC 29 to negate the Dex drain; I think we had said the dex drain multiplied on a crit as well, but I don't 100% recall):
Main-Attack 1 1d20+35 : 5 + 35, total 40
Main-Attack 2 1d20+35 : 2 + 35, total 37
Main-Attack 3 1d20+28 : 17 + 28, total 45 *Critical Threat*
Main-Attack 4 1d20+23 : 15 + 23, total 38 *Critical Threat*
Off-Attack 1 1d20+35 : 15 + 35, total 50 *Critical Threat*
Off-Attack 2 1d20+35 : 16 + 35, total 51 *Critical Threat*
Off-Attack 3 1d20+28 : 7 + 28, total 35
Off-Attack 4 1d20+23 : 19 + 23, total 42 *Critical Threat*
Main-Base damage 1 1d4+18 : 2 + 18, total 20
Main-Base damage 2 1d4+18 : 1 + 18, total 19
Main-Base damage 3 1d4+18 : 4 + 18, total 22
Main-Base damage 4 1d4+18 : 4 + 18, total 22
Off-Base damage 1 1d4+12 : 4 + 12, total 16
Off-Base damage 2 1d4+12 : 2 + 12, total 14
Off-Base damage 3 1d4+12 : 4 + 12, total 16
Off-Base damage 4 1d4+12 : 1 + 12, total 13
Main-Fire damage 1 3d6 : 2, 6, 6, total 14 (halved: 7)
Main-Fire damage 2 3d6 : 6, 1, 2, total 9 (halved: 4)
Main-Fire damage 3 3d6 : 3, 4, 2, total 9 (halved: 4)
Main-Fire damage 4 3d6 : 1, 4, 1, total 6 (halved: 3)
Off-Fire damage 1 3d6 : 5, 1, 6, total 12 (halved: 6)
Off-Fire damage 2 3d6 : 4, 1, 4, total 9 (halved: 4)
Off-Fire damage 3 3d6 : 4, 2, 6, total 12 (halved: 6)
Off-Fire damage 4 3d6 : 4, 3, 1, total 8 (halved: 4)
Main-Shock damage 1 1d6 : 3, total 3
Main-Shock damage 2 1d6 : 3, total 3
Main-Shock damage 3 1d6 : 6, total 6
Main-Shock damage 4 1d6 : 6, total 6
Off-Shock damage 1 1d6 : 4, total 4
Off-Shock damage 2 1d6 : 4, total 4
Off-Shock damage 3 1d6 : 6, total 6
Off-Shock damage 4 1d6 : 1, total 1 (http://minmaxforum.com/index.php?topic=16230.msg335249#msg335249)
Dex Drain 1 3d6 : 2, 3, 4, total 9
Dex Drain 2 3d6 : 3, 4, 6, total 13
Dex Drain 3 3d6 : 3, 6, 6, total 15
Dex Drain 4 3d6 : 6, 5, 1, total 12 (http://minmaxforum.com/index.php?topic=16230.msg335250#msg335250)
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Critical Confirmation:
Main-Crit on 3 1d20+28 : 20 + 28, total 48 *Crit*
Main-Crit on 4 1d20+23 : 3 + 23, total 26
Off-Crit on 1 1d20+35 : 10 + 35, total 45
Off-Crit on 2 1d20+35 : 13 + 35, total 48
Off-Crit on 4 1d20+23 : 10 + 23, total 33
Main-Crit damage 3 1d4+18 : 3 + 18, total 21
Main-Crit damage 4 1d4+18 : 4 + 18, total 22
Off-Crit damage 1 1d4+12 : 1 + 12, total 13
Off-Crit damage 2 1d4+12 : 2 + 12, total 14
Off-Crit damage 4 1d4+12 : 3 + 12, total 15 (http://minmaxforum.com/index.php?topic=16230.msg335250#msg335250)
Searing Aura damage 2 2d6 : 5, 6, total 11 (halved 5) (http://minmaxforum.com/index.php?topic=16230.msg335251#msg335251)