Cloak of Darkness (or shadows or something, I'm no good with names)

Giants belt + Negatron cloak.
With Sunfire Cape's passive, but black/ purple. (They wouldn't be able to stack)

dumb item i think

NC=negatron Cloak

Eh, I don't quite think they'd do a "flipside" of an existing item; I assume your goal here is another health + MR item? I agree we need an MR version of Randuin's or FH; however, I don't think we'll see that anytime soon since MR is a wee bit stronger than armor at the moment.

I'd kinda like to see them bring the stormhammer or whatever it's called from Dominion and PG to SR; it's a nice "MORE AD, Less HP" version of FM.

If you give a pure MR + Health item you effectively remove mages from the game, specifically burst mages.