RAILGUN_ uses EdDSA signatures over BabyJubJub curve, and then verifies the signature within the snark proof. This architecture allows the signature to be generated elsewhere and the private key doesn't need to be present to generate the snark proof. This makes it particularly good for MPC setups since it can be used in FROST and other similar signing schemes. Many privacy projects don't have private key separation via signature so no MPC support, but RAILGUN does so people can build great multisig and MPC features.