(It’s a character description originally intended to be used as a writing prompt. Please don’t complain to me if you find it less than exciting, because I’m just using it to explain correct grammar and punctuation.)
How it ought to be written:
This race of elves is dusky-skinned and has warmly colored eyes. They are easily addicted to certain substances. They lack inventiveness; their technology and knowledge are ages old. Their history conceals a great secret.
Why it ought to be written that way:
The noun that goes with the verbs in the first sentence is race, not elves: This race is… and has…
Don’t hyphenate a compound adjective containing an –ly adverb.
A dash is used to indicate an abrupt change within a sentence. There is no such abruptness in the third sentence. In fact, there’s a clear connection between They lack inventiveness and the rest of the sentence. Use a semicolon instead of a dash, or replace the dash with a comma followed by and, or make the sentence into two sentences (although the connection will be less clear if you choose this third option).
I got rid of all because it’s an unnecessary word.
When you have a compound subject (in latter part of the third sentence, the subject is technology and knowledge), you’re talking about more than one thing, so you need a plural verb to go with the compound subject. Replace is with are.