Dies to Removal

arcanis the omnipotent sits at the unique intersection of card draw and good target for untapping.

Also if you can swing it I've always wanted to see how phyrexian processor worked in commander, and combining it with derevi seems like a natural.

There aren't as many effects that directly target players as you would think. Lots of the things you would think it stops are actually "each opponent". It's only major contributions are stopping edicts and some discard effects.

I can say from experience that witchbane orb and ivory mask won't do what you think they will.

It has been my noticing that derevi tends to helm a lot of "toolbox" style decks, and she's good for it, at her very worst she's a 4cc chump blocker on demand, and that's not even trying to use her even moderately effectively.