1 Blightsteel Colossus Not only is Blightsteel Colossus a massive artifact creature but with infect, it comes with an alternate win condition too
That said, its a strong red planeswalker, and if theres a reanimator deck in Standard using cards like Builder's Talent, it can see some play
Generally you want to make sure you have a two or three-color identity for a theme like this, and remember that the majority of your good enablers will be in Grixis colors: Brallin, Skyshark Rider plus Shabraz, the Skyshark Raffine, Scheming Seer Chainer, Nightmare Adept Rielle, the Everwise Soul of Windgrace Amber Gristle OMaul plus Agent of the Shadow Thieves (or Criminal Past) Slogurk, the Overslime Despite their contrarian approach to the Commander metagame, discard decks are capable of some truly disgusting lines and offer a huge range for individual expression
But the problem with having Kardur in the command zone is that you lose that element of surprise that you wouldve gotten from playing him from your hand