"Challenge extended.” = I dare you to to something . Example: gambling, a race, a duel. “Deal!” = I agree “Challenge accepted.”= I accept your dare and I will do it.

Nothing special. The two words go together. You "extend" a challenge to your opponent. That is how you do it.

hm... if you would be playing a card game for money.... that could mean something " the bets are raised"... anyway i think it means that a challenge/ game continues ...