To show how ridiculous Old Scratch's Doom Mojo is, let me show you all a turn 3 win (can be achieved by swashbuckler and privateer) that is nearly unpreventable. It has a 95%+ win rate against anything that isn't running the same or similar strategy. For this, you'll need Friar Sand's Hirigama, Baron Samedi's Standard (Hoodoo Bundle), and 1-2 boon pieces for privy (2 makes it more consistent, 1 gives you more flexibility should your combo not win instantly) or Fog for swashbuckler. You'll want to bring all defensive melee companions besides Scratch, so the best call is to bring Contessa and Rat. This strategy revolves around abusing the invulnerability the Hirigama's unique power provides.
Round 1: Swashbuckler should fog and reposition their units to set up for a banner placement the following round. Scratch needs to be adjacent to the tile you want to put the banner on. Privy can either banner or boon, doesn't really matter. A combination of Rat's hold the line and Contessa's Gallant Defense should keep your pirate, the banner, and Scratch alive for the two turns your enemy will have to respond to you (either turns 1 and 2 or turns 2 and 3)
Round 2: Both classes should do what they did not do the previous round (you should discard aggressively on round 1 to ensure you have all 3 pieces of your combo). Reposition units as necessary to block your opponent's ability to break the banner.
Round 3: Use the Hirigama's power, then use Scratch's power. The other 2 units can pretty much do whatever.
With doubly stacked weapon power buffs (fog/boon and banner) that aoe just devastated your opponent's team, while your team has taken no damage. If they somehow did survive, it doesn't matter. You're so ridiculously far ahead that you essentially can't lose (you still have all 3 of your scratch buffs, all of Rat and Contessa's guaranteed attacks, and almost all of your pirate's powers).
As I said in a previous post, the only way to beat this is with high movement range companions that can disrupt the combo before it goes off. However, the scratch user's defensive units, and if they're a buckler, their fog, make this nearly impossible to do.