Unlimited mode lets you keep playing after the daily puzzles. Pick any mode (Classic, Quote, Ability, Emoji, Splash or Imposter) and every round gives you a new random champion. When you find it, start another round straight away.
Unlimited rounds don't count toward your daily streak or stats, so it's a safe place to practise. Your daily puzzles are still waiting for you, and a new set arrives every day at midnight UTC.