I think you went overboard in response to Alxmhn1's comment about needing to fix your mana...idk ...this is the 1st and only time I've seen your list... I can say that 11 ramp cards is excessive..unless you're playing a landfall deck or something....i'd cut 3 of those. Additionally, you have 19 (GASP!) lands that etb tapped and 2 more that conditionally do/don't etb tapped....good gawd man. 6 etb tapped is preferable, 10 at the absolute most for even the most budget deck... you can use basics too you know :)

Your current weakest links appear to me to be Vision Skeins, Convolute, Sign in Blood and Servant of Tymaret.

Some other cards possibly worth considering; Everlasting Torment, Forsaken Wastes and/or Sulfuric Vortex .. don't know how popular lifegain decks are in your meta but I love having one deck that wreck's them. Fevered Visions, Ebony Owl Netsuke, Guard Gomazoa, Magus of the Wheel, Jushi Apprentice, Liliana's Caress are some of my favs...additionally Breathstealer's Crypt, with your low creature count can just break aggro decks with all your wheels. Another thought is Warped Devotion when combined with megrim/lili's caress + cards like AEtherize or Cyclonic Rift are brutal (and may cause table flips) if you wanna be that dickish.

anyways...hope this helps, gl & hf

since you said you want some advice on pieces to pick up first, id try to pick up the leyline helm combo since I find it good to typically have 1 wincon that doesnt require the commander and 1-2 wincons that do (in most decks anyway). The next thing is fetches. They are cheaper now with MM3 so i'd pick them up regardless, but your call with this. After that comes wheels and waste not. Next, I'd pick up d tutor and v tutor (understanding that imperial seal is VERY expensive).

I assume you want to remain friendly with your playgroup (getting targeted sucks), so id suggest anvil of boggardin, dictate of kruphix, font of mythos, etc.

If you want to look at the most fully optimized build for commander(100% spike level), i'm sure there are many lists here or on mtgsalvation.

Day's Undoing should not be in this deck. You can only cast it if you have Leyline of Anticipation on field to play it on another player's turn- meaning it is a functionally worthless card without another card (and you run no tutors). To explain: As part of ending the turn when resolving Day's Undoing, all objects on the stack or waiting to go onto the stack are exiled. They don't resolve, so even with Nekusar on board, this does 0 damage without a way to cast it on someone else's turn.

Drop it ASAP for Winds of Change or Whispering Madness. Wheel and Deal isn't a bad option either.

Is there a reason you're using Megrim over Liliana's Caress?

Waste Not may potentially be a good call, as well.

PookandPie I want to have both cards for redundancy, I just don't own Liliana's Caress just yet. The other cards will be added to the list, thank you for your help!

I would cut Nullify or Stoic Rebuttal for Counterspell, since they are strictly worse. Master of the Feast is another great creature for Nekusar, a 5/5 flying body for 3 can be a great deterrent. I would also run a few more basics, especially since you only have 2 swamps and almost a third of your deck is black