Can I use Chosed Champ Teemo and hide it when I play?

Yes, you can hide your Chosen Champion Teemo. According to the rules and FAQs, you can perform the Hide action directly from your Champion Zone.

Here are the specific requirements to do so:

1. Timing: You must be in an Open State during your own turn.
2. Cost: You must pay the cost specified by the Hidden keyword, which is one rune of any domain ([A]).
3. Action: Hiding is a discretionary action (Rule 421.2). Since your chosen champion is in the Champion Zone, the game treats this as a valid source for the "Hide" action.

Important Considerations:

• Not the same turn: Per RiftJudge FAQ #6210, a card cannot be played on the same turn it was hidden; you must wait until a subsequent turn to play it from its facedown position.
• No "Move to Hand" required: While some older rulings suggested you needed to move the champion to your hand first, the current rules and FAQ (#9031, #6430) explicitly allow you to hide the unit directly from the Champion Zone.
• Battlefield: You hide the card facedown at a battlefield you control that does not already have a facedown card hidden there.

This is my interpretation based on the provided rules and FAQ #9031. No official rule chunk explicitly contradicts this now-standardized interaction.