I wonder if there is a possibility for dragons and other mega beasts to be intelligent and have an alignment.
Reading legends I believe dragons are already antagonists with bases in lairs, so further villain capability should be suitable.
Other villains could be : giants, forgotten beasts, ?eventually(sea beasts and creatures), great collectives of lesser creatures (eg. imps?)
single or collectives of were-creatures? greater-spiders.
> Villainous activity could be capturing and kidnapping people and imprisonment in lair, possibly as ransom for treasure (or to eat)
> They may hypnotise and control creatures : to spy on settlements (maybe to later attack or take over)
> They may gather a willing (cult) or unwilling following of people, and possibly use these to attack, defend themselves or spy, or make themselves powerful
> They may menace and threaten a settlement or people in return for tribute, or they may bribe with treasure or a hypnotism for influence
> They may cause trouble for the sake of it, scheme out of nature or enjoyment
> they may hold grudges on a general population
The obvious dragon villains are talkien's Smaug, Fafnir from norse mythology and Beowulf dragon.
They seem have a thing for treasure and greed for wealth
So other villain beasts could be fixated on power and influence (tribute / following), or causing violence and damage, or hunger for food,
or hunger for a following (belief / worship)
they could also be motivated by jealousy (of wealth/reputation), or out of alignment (eg enmity to followers of a deity)
They may just hate certain kinds of creatures eg. underground beast hating dwarfs from surface