First off, twenty villains, while awesome, is not nearly enough! So many great villains left to make Hasbro. They could do a Bring On The Bad Guys wave for a few years and still not make a big enough dent in the Legends villain deficit.
All classic versions unless stated otherwise.
Initial Top 20 Villains
1. Doctor Doom classic Kirby or Byrne
2. M'Baku/Man-Ape make it fan channel Jessie
3. Wizard w/anti gravity disks
4. Trapster/Paste Pot Pete multiple glue effects, glue gun
5. Mandarin silver age, ok to lose the "M"
6. Attuma
7. Surtur Simonson style with Twilight sword
8. The Collector old guy version
9. Stegron classic Lizard size not huge
10. Crimson Dynamo Bukharin
11. Titanium Man Bullski
12. Madcap love this goofy villain
13. Air-Walker finish the last main herald of Galactus
14. Supreme Intelligence even though he'll just be a statue, I still want him. Give him the crackly Kirby stuff and I'm good.
15. Annihilus needs a redo, not so pink
16. Puppet Master w/tiny puppets to manipulate (The FF and Hulk would be perfect)
17. Volcana finish the last main original Secret Wars villain
18. Darkoth such a great design he'd really pop on the shelf
19. Abomination correct size, colors, and head sculpt this time please
20. Zzzax w/classic Wendigo apology headsculpt pack in for the previous Wendigo baf.
Amazon 5 pack
Serpent Society: Sidewinder, Diamondback, Anaconda, Bushmaster, and Death Adder.
While I want them all, these five would be the most essential members yet to be done.
I easily came up with 15+ other villains right off the top of my head. Sucks to leave them and so many others off the list.
Come on Hasbro! Bring On The Bad Guys!