First, if you don't play Multi=2♦ yourself, forget this defense. It is not for you. But if you play multi-2♦, you may find this as much fun as I do.
What is multi 2♦? An opening bid of a weak two in either major. Then others add other possiblities, like big balanced hand, or acol 2 in either minor, or strong 4441 pattern with any singleton. Different people have different theories, like making it always weak two in a major (only), so that 2♦ is passable....
Ok, here the system I found and like. It is called multi-versus-multi, the following link will open Chris Rydal's descripton of this defense.
multi-vs-multi
So they open 2♦, most likley they have a major. Since ther bid shows potentially a lot of hands, this system does too. A double is an overcall in either major, or a big balanced hand, say 19-22 or 20-23, or three suiter with 19+ (with weaker three suites, pass first).
So here after a double, they don't know what your hand type is and you don't know their suit. But if partner can pass 2♦X you will find out thier suit real quick... now both you and your partner use Takeout Doubles of their suit...This is also true if responder bids a major over your double...
LEt's look...
(2♦)-X-(2♥)-X here, your partner's double is "negative" kind of thng showing ♠'s. IF you have ♥'s or huge balanced hand they are opener are in some trouble. IF you have ♠'s you are ok, too, you can simply show your suit and relative stregnth wth your bid.
Ok, if 2♥ and 2♠ are no longer needed over 2♦ to show your suit when you ahve a major? Waht are they? Well.... here is rest of structure...
- 2♥ = balanced hand, say 15-18 or so. Partner with ♥ can pass, or can correct to 2♠, also to play
- 2♠ and 2NT = minor suit transfers, with super type accepts by partner to show some values. You might play something like this over your own 1NT openings.
- 3♣ and 3♦ = preemptive type bids, not forcing. And here they don't know if they have a fit or not and what opener's major is.
- 3♠/3♥ = michaels, showing like 5-5 in bid major and a minor
- 3NT = big balanced hand, bigger than the immediate double, obviously need stoppers in both majors
Anyway this is fun to play. Take a look at Chris's webpage (link above) for more examples and a great write up.
Ben