The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

...whereas an elf
is an IMMORTAL, tall warrior.
The Big Bang Theory Season 1, Episode 6

In the words of Khan Noonien Singh
in the IMMORTAL Wrath of Khan:
The Big Bang Theory Season 3, Episode 5

Because he's neither tall nor IMMORTAL,
and none of us could be the Flash.
The Big Bang Theory Season 1, Episode 6

And my IMMORTAL soul
gets cast down
Westworld Season 2, Episode 2