Siren is a true 5A string trick. It starts with a seemingly simple double or nothing, then goes into a barrage of simultaneous underpasses and counterweight transfers.
Start with a 5A Double or Nothing. Pop the yoyo out for a dismount and drop the counterweight. The should be traveling in opposite directions.
Land a bottom mount with the yoyo on the middle finger. Do a big pinwheel with the counterweight then on its second revolution thread it in the gap of the yoyo. Then at that precice moment, dismount the bottom mount, landing the yoyo onto the string already there from the counterweight.
Perform an underpass and cross your hands to drop the counterweight (thus un-mounting the yoyo).
Flip the yoyo in the opposite directions, perform one pinwheel. The counterweight should hit around the back of the non throw hand forearm to redirect its trajectory.
Now that everything is traveling in the same direction, grab the counterweight in the throw hand as it comes around, land the yoyo on the non throw hand index finger. You should be in a fake 5a double or nothing.
Drop the strings, except the counterweight, on the throw hand. Toss the mounted yoyo up and over. Toss the counterweight up and over. It should look like a mounted version of angel wings. The counterweight needs to come around the front of the back of your hand. Catch the counterweight and pull everything apart.
You should be in a trapeze. Bind and return.
Tricks to know before Siren: