Your deck appears to be about 20 years old (that's not in any way intended to sound insulting) and SO many cards have been printed since then.. A lot of our suggestions really depend on a) your budget and b) your typical playgroup. In other words, are you looking for our theoretical suggestions or more reasoanble ones? Also, are you usually playing duels or multiplayer?
There used to be a very good primer about Suicide Black on this very site but it seems this did not survive the migration of this site to the Curse platform. That's a pity.
I've run a dedicated Suicide Black deck since at least 2003 so I'm happy to help you here if I can. I've tried a lot of things over the years.
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Nude Eternal Witness?
Wouldn't they have to edit that for the Chinese markets?
Only if she had skulls for nipples.
4x of each (budget permitting) I probably wouldn't run *8* strip mine effects but I currently run 5 total in mine. The idea is hopefully hit a land and a card or two. Knocks a lot of decks back on their heels. If you draw multiples, a lot of decks are just DONE right there. This is how Sui-Black wins a lot of games--cheese them out. Oh, and Sinkhole has finally been reprinted. It's a lot cheaper now!
Now, Thoughtseize is a pretty damn expensive card (as is Wasteland) for not a huge amount of upside over the cheaper alternatives. Honestly, I think you could easly replace TS with Inquisition of Kozilek or even Drill Bit (but Inquisition is 100x better). To be perfectly honest, Duress is great card already.
As far as beaters go, I'd update things a bit, yeah.
Hypnotic Specter is probably a bit long in the tooth these days but still serviceable here. I think Prowler is just perfect here. He applies pressure on them either way. Confidant is a no-brainer but expensive. SCrivener or Ruin Raider are decent budget options. The biggest creature upgrade of all probably has to be this guy but you have to sequence things properly. I run four. He's been reprinted a few times now so he's not too expensive either.
As far as getting your own life down, I'd probably recommend stuff like: