(1) Roman Key Card Blackwood.
(2) One key card.
West leads the ♥3. East wins the ♥A and shifts to the ♦5. Plan the play.
You need 3–3 or 4–2 clubs (84%). The two traps are not to run the ♥Q to take an unneeded ruffing finesse at trick two nor to take a practice spade finesse.
If both follow when you cash a second diamond, cross to the ♣A, ruff your last heart with dummy’s remaining trump, ruff a low club, cash your remaining diamond discarding a spade from dummy, and run the clubs. With diamonds 3–2, you can handle 5–1 clubs as well.
Thanks to Jon Shuster of Gainsville FL for this one.
Update: Reader Stephen Cooper of Toronto ON pointed out something that I overlooked.
Instead of crossing to the ♣A at trick two, declarer should play the ♣K and a club to the ace. That way if clubs are 5–1, declarer can discard two clubs on the ♦K J and hope for a lucky heart position. For example, East might hold the ♥K Q (x) or honor doubleton, or West might hold K–Q doubleton as you plan to lead low to the jack and then the ace. This is roughly an 8% improvement over the original line of play.
West leads the ♠J. How do you play at matchpoints? At IMPs?
IMPs: The play in a knockout match is something else. For a 30-point (1-IMP) investment, it pays to try to ensure your contract rather than play for the overtrick, which requires 3–3 clubs. In addition, your opponents at the other table may not have reached a slam, making it even more important to bring this baby home safely.
In order to guard against the same player holding four clubs and five diamonds, cash the ♦K J at tricks two and three, but this time, duck a club — the key play — at trick four. Win the heart or spade return, cross to the ♣A, discard two hearts on the ♦A Q, return to your hand with a spade, and cash the ♣K Q. As long as clubs are 3–3 or 4–2 (84%) you have 12 tricks.