Double Scorpion Solitaire has the same mechanic as all the Scorpion Solitaire games (and Wasp - which is sometimes also known as Easy Scorpion).
Groups of cards in whatever order can be picked up and placed wherever the top card in the group allowed.
Every card from both decks is dealt. There is no Reserve and no Stock pile. Simply put, there are a large number of cards on the screen!
The Tableau has ten columns. The first four columns contain eleven cards each, and the remaining columns contain ten.
This enables you to move large groups of cards around. This makes for some interesting gameplay. It also requires a lot of screen space, so this game is best played using the full screen.