Blue Cards
Mindlink Mech - This is 1 mana more than Smuggler's Copter but does something similar to ensure Sygg triggers. And can be crewed by Sygg alone which is relevant. Importantly, it can also be crewed by something else in order to double up on triggers or just making something bigger. I think I like it enough to try it out.
Moon-Circuit Hacker - I don't really like looting effects in this deck. I think this is a solid card, and the first time it enters it is a straight draw, but I think I would rather stick with what I have so far than try to find room for this.
Prosperous Thief - This works with Sygg, Dauthi Voidwalker, Brazen Borrower and Yuriko which is nice. It can potentially generate 3 Treasures per combat (though that it extremely unlikely). I wonder if adding it in as a form of ramp is worthwhile? I am not the biggest fan of temporary ramp like this can it can make things a little more explosive. My initial thought is that I want to pass on this but I might come back to it.
Black Cards
Invoke Despair - This is a little higher on the curve, but it seems like it is probably very often something that gets rid of 2 permanents, has the player lose 2 life, and we draw a card. Or, at least, they will lose 4 life, sac a permanent, and we draw 2 cards.
Junji, the Midnight Sky - If only it was the players losing 3 life...I tend to keep this deck very low to the ground, but if I wanted to expand the top end a little, I don't think this is a bad choice. It eats away at hands if I want it to or I can get some other big creature from someone if I needed it to. This deck doesn't do a lot with sac outlets (though I could just point a kill spell at it) so that might make it tougher to go off when I want it to. Still looks like a fun card.
March of Wretched Sorrow - This is a kill spell that can hit Walkers and gains me life. However, I think the mana cost, or amount of cards to exile, is just too high to be worth it. I like the card and like the design, but it is just not quite good enough.
Nashi, Moon Sage's Scion - This seems like a solid addition. He is 3 power which is relevant, 3 mana (I don't think I will ninjutsu him too often), and is a "draw" and "cast free stuff" all in one. While the life payment could be troublesome, I think the overall effect, and even just using it to hit a land, is pretty fitting for the deck. I think I will try to find a spot for him.
Tribute to Horobi - This looks really cool. It is a bit of a gamble, but Sygg being able to block the tokens means I won't get hurt by them (and what is 1 damage anyway). The main issue actually ends up being if the opponents are just smart enough to attack into each other with the rats so I don't get any. But if they don't do that, I can get up to 6 rats which can then be used as fodder for the back face to draw cards. And, even if they do that, I still get a 3/3 Flyer with Haste that can sac something else. I think this could be a good card but it really needs to be played to see how it works out in practice.