Multi Attack and Extra Attack Chance affect Special Skills of MH when using Discordance Mythic. depending on the Skill, it either gives extra attacks or increases damage done with the one attack. either way, it’s doing more damage.
if using a Gauntlet with Discordance Mythic, Twister would do 150% weapon damage, be affected by Attack Speed for how fast you can cast it (using APS), use Mana Cost of Blast, and is affected by Multi Attack and Extra Attack Chance. you would still put skill points into Twister, but the 1% per rank Cool Down wouldn’t work.
Blast would do 400% weapon damage, use mana cost of Twister, have Twisters Cool Down and would be affected by Cool Down. Skilled Mythic will still work work on Blast.
you can get up to Multi Attack +4. Multi Attack would usually only work on Blast, the Primary Skill of Gauntlet.
Twister as Special with 40 Skill Points and +60% Cool Down can be cast every 1.2 seconds, lasts for 5 seconds, hits for damage 5.6 times a second, and does 1200% weapon damage per hit. that comes to about to 5376% DPS weapon damage.
Twister as Primary with 40 Skill Points, +60% Attack Speed, and Multi Attack +4 can be cast 2.4 times a second and lasts 5 seconds, hits for damage 5.6 times a second, and does 450% weapon damage per hit. that comes to about 18144% DPS weapon damage with Multi Attack (not sure how accurate I am with this).
now, I heard Specials can only go as fast as 0.5 Cool Down. when using Discordance, but I haven’t tested it. but it looks like using Discordance, Twister could have more DPS as a Primary Skill than as a Special.
here is a post on the subject.