I agree with majofa with scorpion’s weakness to shields. The first question you need to ask when using scorpions is how you want your deck to play. Scorpions in general are useful for early damage and then consistent poison damage during the remainder of the game (pray you don't see purify).
I personally like using scorpions as a quick initial damage dealer and then only consider what poison they put out after about turn 3-5. If your opponent has a shield, it will be out by then and your scorpions will be worthless. The scorpion’s base damage of 2 is normally not enough to punch through much of anything. A good draw can net you 10 poison by turn 5, average, around 6. Building a deck with this philosophy, you can then either stall [Heal, Empathic Bond, Miracle, Sanctuary, Diamond Shield], get rid of the problem [Momentum, Explosion, Steal, Butterfly Effect], or switch to heavier praetors [Jade Dragon]
If you want speed, try the deck below. You'll either win quickly, or be shut down. The main meat of the deck is the interaction of the scorpions, frogs with Epinephrine. The explosions help clear out any unwanted shields.
7ac 7ac 7ac 7ac 7ac 7ac 7ac 7ac 7ac 7ae 7ae 7ae 7ae 7ae 7ak 7al 7an 7an 7an 7an 7an 7ao 7ao 7ao 7ao 7ao 7dm 7dm 7dm 7dm 7dm
Note: Epinephrine the right target. Scorpions do more damage than frogs after 4 turns, 5 turns against a -1 damage shield. Frogs are always better against anything bigger!
Frogs vs. Scorpions; Epinephrine, No Shield
Turns | 1 | 2 | 3 | 4 |
Giant Frog | 11 | 22 | 33 | 44 |
Scorpion | 8 | 18 | 32 | 48 |
Frogs vs. Scorpions; Epinephrine, -1 Damage Shield
Turns | 1 | 2 | 3 | 4 | 5 |
Giant Frog | 8 | 16 | 24 | 32 | 40 |
Scorpion | 4 | 10 | 18 | 28 | 40 |