Yeah I'm not feeling the Topher as Venom casting.
Actually I'm having a hard time believing any of this until it comes from a more trustworthy source. I've never even heard of Freeze Dried Movies.
3 major villains in 1 movie? Talk about overkill. No way can it be done well enough in a reasonable running time. Unless they use Sandman stupidly and have him knocked off early in the beginning, pre-opening credits sequence type of thing. But that would suck.
Cramming all these villains in makes this franchise start to smell like the old Batman franchise, and we all know how great those were.

I cringe at the thought of Sandman saying "You're not sending ME to the SANDBOX!"
Let's see if any of this true or not first though...