No, I did mean Entangle. Elves are nimble and have a connection to nature, so they can easily escape twisting vines. Then again, that is maybe more apt for Wood Elves than for Dark and High Elves. Your suggestion of Web is better, since it’s again mana related I also like the immunity to charm @Anchovies mentioned, so why not bundle it all together?
Elven Willpower: Immune to Charm, Mana Burn, Mana Drain, and Web.
That does sound like a nice overall trait that would fit all three elf races I think!