Phyrexian Arena if you got it. +1

I've been desperately trying to find one from people at my local shop, no luck yet.

take out Tyrant of Discord and Dread Slaver

And what? Have holes in the deck? Tyrant of Discord is fantastic on Mimic Vat. Dread Slaver can net me other peoples creeps early game or late game if he has Unscythe, Killer of Kings

OK I'm not trying to be a jerk and keep in mind you don't have to agree with me, but I feel like you are not evaluating Tyrant of Discord and Dread Slaver very well.

Yes, Tyrant of Discord is godly with Mimic Vat, but you don't add a card because it happens to be good with ONE other card in a 100 card deck. Without Mimic Vat, Tyrant of Discord is usually just gonna kill off a land (one land in a sea of tons of lands,so it essentially makes little difference) or you might get lucky and hit a few non-land permanents, but the times when it is truly worth will not be occurring often. If you need an extra card slot then Tyrant of Discord is fine, but I can already see you have other cards you can add that will help you more. Tyrant of Discord isn't that bad though, so I can understand keeping, its just not what I would do.

Dread Slaver, however, seems to not deserve a slot in this deck at ALL. No one will attack with a 3 toughness creature when Dread Slaver is out, so you will never get a dude with it. You might deter a few attacks but typically it will not be worth it in the long run. If you do get the Dread Slaver to large sizes, it will just be targeted with removal and never really do anything, but waste your opponent's removal. Overall I can't see why Dread Slaver would be worth it.

Well, with the extensive ways I have to tutor, keeping Tyrant of Discord just for Mimic Vat really doens't seem like that poor of a choice.

What would you suggest I remove Dread Slaver for?

I have a question, I'm trying to make my own Thraximundar Zombie EDH. Why Hex Parasite other than to take off the undying if you happen to have out Mikaeus, the Unhallowed?

Some other helpful cards might be Minamo, School at Water's Edge. Get to attack with Thraxi when he comes into play AND still have him block potentially. Sepulchral Primordial also, while not being a zombie, is excellent for graveyard shenanigans. Combined with Mimic Vat is just plain awesome. I also agree that Tyrant of Discord could come out for something like the Ashenmoor Liege or Cover of Darkness you're trying to put in.

I'm on a bit of a budget but any feedback would be appreciated if you're interested: Thraximundar's Guide to the Galaxy.

I have trouble dealing with planeswalkers in my playgroup, so Hex Parasite serves as a pretty reliable way to keep them down.

I think I'd be more tempted to pull Dread Slaver for Cover of Darkness and maybe Tyrant of Discord for Stolen Identity as to copy my rocks.

This deck has been 2 years in the making and runs very very well, I'm not trying to upset this balance I've worked so hard to create.