Torrent Elemental with Whip of Erebos is a great idea, and I like it!! Do you think Ashiok, Nightmare Weaver is good for this kind of deck? I feel like you'd be better off with Nighthowler or Nemesis of Mortals

doanenut, I don't think I want Nemesis of Mortals due to the large amount of removal and random chump blockers everyone seems to have, meaning a large guy with no evasion or resiliency isn't very good right now. However, Nighthowler is definitely worth considering, especially since bestowing it gives some resiliency and Torrent Elemental can force it through. I'll definitely give it a shot, though I think having Nighthowler will mean I need more Commune with the Gods, not something I'm a huge fan of.

In regards to the two maindeck Ashiok, Nightmare Weaver, they're not necessary to the deck by any means, but I played one in the main and one in the side last fnm and it's just so good in a number of matchups that I want to try 2 in the main. Those slots are flexible though, I would swap them for Hero's Downfall, Pharika, God of Affliction, Sultai Charm, Reclamation Sage, Commune with the Gods or Bile Blight depending on what you're expecting.

Looking at this deck only one thought comes to mind, why aren't you playing heroes downfall? At the moment you have no way of killing planeswalkers other than hitting them with enough creatures, which can be quite hard against token decks, control decks, burn decks, and even creature-kill decks, since killing your creature will delay the death of the planeswalker for at least one turn. I suggest that you take out one or two murderous cuts and add in some heroes downfalls, as well as some counterspells just in case they play something big. It seems to me that your deck does badly against control decks, since you are often playing big spells like Sidisi, Torrent Elemental, and above all, Whip of Erebos. Admittedly, the Whip of Erebos does work very well with Torrent Elemental and Sidisi, since it brings them and cards they put into the graveyard back to the battlefield, but if the Whip is destroyed, exiled, of countered, your creatures would become very susceptible to creature-kill spells. The best way to avoid this is to add counter spells to your deck, thus making it more durable.

Ouranos139 The reason I'm not playing Hero's Downfall in the main of this deck is because of how powerful my creatures are and how well they push through to the opponent or their walkers. In addition Murderous Cut can be played in addition to a second spell a lot earlier than downfall, allowing for more tempo swings in my favor. I do also have Thoughtseize to deal with something I may not be able to otherwise. Cut also has the upside of exiling Torrent Elemental in the absence of whip.
I also don't think having counterspells in the main is a good idea, since it would decrease our creature count for sidisi and would mean we would have to leave mana up on out opponents turn, something this deck can't really afford to do much of considering the proactive strategy.
I do however like having both downfall and some counterspells in the side in case we need to be the control deck post board or protect whip like you said.
In the event we cant protect whip our value based midrange plan should still serve pretty well.

if you don't like Commune with the Gods you still have the choice to consider Taigam's Scheming or Nyx Weaver!

Well it's not that I don't like Commune with the Gods, it's just that I don't like taking a turn off to not affect the board in the current standard environment. Though I guess it's interaction with Sidisi means it could not be as slow as I think it is. I actually like Taigam's Scheming less because it's card disadvantage, we're not a combo deck and commune finds Whip in a better way than it does. Nyx Weaver on the other hand is something I want to try. I feel like this deck could use a Regrowth effect and the synergies it has with sidisi are super cool. I just can't help thinking it's suuuuper slow. And that it fills the same slot Ashiok/nighthowler would fill.
Still worth a shot though.