Overcalling after a strong 2♣ opening bid has been made is risky. Since opponents are known to have most of the strength, it is very unlikely that your side has a game, and the risk of being doubled for penalty is high. Tread carefully.
In the absence of partnership agreements to the contrary:
- A double of the 2♣ opening bid or the 2♦ relay is lead-directing since both bids are artificial.
- A notrump bid is unusual notrump, showing the lowest two suits that have not been bid naturally. Therefore, after 2♣ or 2♣ - 2♦, it shows both minors, since neither bid is natural.
- Any suit bid is a preempt.