Here is a basic BUL-KATHOS WHIRLWIND BUILD + VIDEO:
1) Area Damage everywhere, where possible. 150 area damage is good :). Try to get at least 40% cdr and then max AD everywhere.
2) STR Augments for more DPS/toughness
3) 5th Passive: Berserker's Rage/Relentless//Tough as Nails/Superstition
4) ~45CDR required for perma WOTB. All the rest should be spent on Area Damage.
5) Bane of the Trapped can be used instead of Pain Enhancer (almost same results across the rift, worse against Juggernauts).
6) All diamonds in chest/pants for more toughness.
Now for some safer options if you have low paragon/bad gear/no augments (like me).
1) Ignore Pain - Iron Hide. More DR, but much less recovery.
2) Threatening shout - Demoralize. A little more crowds/AD usage and much more Damage Reduction, but much less raw DPS. Useless against RG as well (RG cannot be taunted).
4) Overpower - Killing Spree/Crushing Advance instead of Warcry. Killing Spree is max DPS option (if you can survive)
5) Ancient Spear - Rage Flip, great pulling option for wandering leftover elites. Pretty hard to execute though (for me personally)
6) Battle Rage - Swords of Plughshares - good healing source, but much less AOE damage.
7) Ground Stomp - Wrenching Stomp instead of Warcry = good grouiping/stun skill, but can make you dead in seconds. VERY GOOD for creating density!
Keep in mind that Obsidian Ring of the Zodiac reduces RAMAINING cooldowns of skills "currently on cooldown" by 1 seconds, randomely. So if you have 3 skills on cooldowns instead of 4, it will refresh WoTB faster. Don't spam Falter and Ground Stomp like crazy. If you play without Ground Stomp and use Rage Flip or Overpower (it uses charges with it's own cooldown) for example = Zodiac will refresh WoTB faster (and you need less CDR).
Also one more important thing: Obsidian Ring of the Zodiac has internal cooldown of around 0.9sec/Sheet_Attack_Speed (just like Stricken gem). So with higher attack speed===>faster_ticks_of_WW = you will proc Obsidian Ring faster. This is one the main reasons why we use Pain Enhancer. Higher attack speed===>higher breakpoints===> faster ticks==>faster Obsidian procs.
GR98 CLEAR: https://www.youtube.com/watch?v=nc7fZYMlOzg
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