I just started to put this list together, but....

My group is doing a challenge to build decks under $100, so this is my first try, choosing to use Marchesa.  She's already very powerful, but the modular mechanic just meshes so well with her, and the cards are cheap, so this seemed like the perfect marriage.  Sacrifice modular creatures every turn so Marchesa can bring them right back, then rinse and repeat on each turn.  Death triggers and sac abilities galore, ETB triggers, a massive collection of +1/+1 counters... sprinkle in some removal, lots of ramp and draw (cheap can still be fast), some spell counters and protections... let's rock and roll!

Going with the synergy between modular and Marchesa does two huge things: for one, it allows to you sac modular creatures on every player's turn while Marchesa is in play, amassing a ton of +1/+1 counters on various artifact creatures, and two, it lets you not have to use dethrone and attack every turn to put +1/+1 counters on your creatures, making you less of a target for Marchesa's targeting of the player with the most life.  This also makes you not have to rely on having a lower life total to be able to trigger dethrone, meaning you can play more life gain cards, of which black has plenty of with death triggers.  Ideally, every creature in the deck enters with a +1/+1 counter, unless it's a sac outlet or a death/ETB trigger machine, with a desire for artifact creatures overall.

Grixis only has four creatures with Graft (like Novijen Sages), but they are diiirrrrty with Marchesa sac engines... they allow you to sacrifice creatures that don't enter with counters on them on every player's turn.  After saccing, have the Graft creature's ETB trigger resolve first, then have the other creatures ETB after and get +1/+1 counters from it.  Then sacrifice them all at the end of the next turn, rinse and repeat.  Or use a graft creature to have Marchesa ETB with a +1/+1 counter when she's cast, giving her instant "protection" without having to give her haste.