>>5306312Violet's rare? There's tons of listings on eBay for like $2 more than MSRP with free shipping, and Randall is up on Amazon for MSRP. Syndrome is the only one that looks slightly rare, but there's that villain three pack you can buy for $20 that comes with both Randall and Syndrome along with Davey Jones.
From quick store checking, the Symbiote Spiderman looks like the only tough one to get outside of store exclusive since the Vita version seems to be out of stock or not sold anywhere and eBay just has people selling the thing without the figure itself.
Honestly, from what I've seen the only things tough to come by are things like picture related, and only for specific characters. Jack Skellington really seems to be the only difficult one to find out all the ones released that I can see.