hey there! I recently put together a Marchesa deck of my own (link) if you'd like to take a glace. Mine has a different motif than yours. but you might find something you'd like.

Your deck looks pretty solid for what you're going for. The big thing I have to add is Willbreaker. It's friggin' insane in Marchesa with Unspeakable Symbol. Gain control, sacrifice, and keep. Great tech.

Speaking of sacrifice, you may want to add a couple more means of offing your own guys to make your treason effects a bit more permanent. Altar of Dementia can dump more creatures in the graveyard and Phyrexian Altar is a bit expensive but helps you hit your mana.

Willbreaker would be perfect, that's an awesome add, Phyrexian Altar is in there but I have been considering more sac outlets.