I'm going to be honest, The Scorpion God is not the most efficient or effective commander. He costs 5 CMC to cast,
his ability cost 3 cmc to active and -1/-1 counters are not the easiest to spread or kill creatures without additional support. Now that we squared that up, there are some benefits the ol' Scorp has. He is able to remove indestructible creatures, he can easily avoid commander tax upon death due to his third line of rules, and a 6/5 ain't too shabby as a beater or blocker. Scorpion God can be a lot of fun, but he needs some support to be effective.
Reanimation, Scorpion God and you.
I chose to take this deck in a reanimator direction. Scorpion God's colors are optimal for this theme and being able to bring back creatures, only to kill them and draw off Scorpion God seemed like a good plan. Essentially this deck is a Rakdos Reanimator with a splash of -1/-1 flair.
Ride and/or Die Homies
This deck has some all-star cheap creatures that help facilitate Scorpion God's abilities and the reanimator theme. First off is Fume Spitter, this disgusting little buddy is fantastic. Not only is it able to sacrifice it itself, it puts -1/-1 counters onto any target creature we want! Being able to bring him back and cast him for only 1 black mana is a value we cannot pass up in this deck.
Next up is Festering Mummy, although he is unable to sacrifice himself, he puts a -1/-1 counter onto any target creature once he dies which is almost as good as Fume Spitter. However, if have both Festering Mummy and Fume Spitter on the board, we can start to chain the counters. Fume will sacrifice to kill Festering, who will put a -1/-1 counter onto another creature. If we toss in Blowfly Infestation and/or Nest of Scarabs the fun just continues.
Butcher Ghoul is fantastic with Scorpion God. Undying allows him to return, as long as he doesn't a +1/+1 counter on him and lucky for us, we can negate those with our -1/-1 counters. Butcher ghoul can return over and over if you have your board set up right.
Hex Parasite may seem like an odd choice. We want to put -1/-1 counters onto creatures, not remove them, but hear me out. This deck utilizes both the undying and persist abilities. If we can remove those counters for just 2 life and 1 mana, then we can continue to sacrifice our creatures with these abilities over and over. Additionally, it doesn't hurt to have a way to remove planeswalkers for 2 life and colorless mana equal to the loyalty counters on said planeswalker.
Dusk Urchins is a must in this deck, as well as a Hapatra, Vizier of Poisons deck I would argue. When it dies, you draw cards equal to the number of -1/-1 counters on it and it can put those counters on itself! If you have Scorpion God out when this guy hits 3 -1/-1 counters, you'll draw 4 cards. Now that's value. Additionally, if you have Mikaeus, the Unhallowed out, there's gonna be a lot of drawing cards.
Repeat Offenders
Bloodghast, Nether Traitor and Reassembling Skeleton. These three all have the ability to pull themselves out of the graveyard and all have 1 toughness. These two facts make them perfect additions to use for reanimation with Scorpion God.
Kill a Creature, Make a Treasure
Treasure tokens are very useful a wide variety of decks and why shouldn't Scorpion God get to enjoy some bing?
Pitiless Plunderer and Gadrak, the Crown-Scourge are powerhouses in this deck. Creatures on your board and opponents boards will be dying if you can get some pieces together, so both of these cards seek to make you more treasures to use to active Scorpion God's ability whenever needed.
The Ozolith
The Ozolith is just pure value in this deck. It allows you to put the -1/-1 counters that killed your own creatures aside to use them later. You can accumulate these counters to drop onto an opponent's big creature or just more draw with Scorpion God, or make more insects with Nest of Scarabs. It is also only 1 colorless mana.
Deathbringer Thoctar
Deathbringer Thoctar is an absolute monster in this deck, as we have our creatures dying a lot. If you pair this beast with Basilisk Collar, he is effectively a machine gun to just destroy creatures all over the board. If you add in Everlasting Torment, now we are killing creatures with -1/-1 counters and I think you guys get it by now.
This is probably my favorite deck that I have ever built and it is incredibly fun when it can get rolling.
I'll list some syngeries and combos below (there may be more than listed):
Syngeries and Combos:
1) Mikaeus, the Unhallowed + Murderous Redcap + Sacrifice Outlet = Repeatable sac with damage.
2) The Scorpion God + Nest of Scarabs + Blowfly Infestation + One creature on board = Insects and draw as long as there are targets to put the counters on for Blowfly trigger and die from those counters.
3) Deathbringer Thoctar + Basilisk Collar = Machine Gun Zombie Beast and Lifegain
4) Deathbringer Thoctar + Everlasting Torment + Nest of Scarabs = Many Many Insects
5) Deathbringer Thoctar + Basilisk Collar + Everlasting Torment + The Scorpion God = Creature Removal and Lots of Draw
6) Goblin Sharpshooter + Basilisk Collar = Machine Gun Gobbo and Lifegain
7) Yawgmoth, Thran Physician + Nest of Scarabs = Insect token engine, death triggers, -1/-1 counters and card draw, but will lose 1 life per creature.