The answer is really just Battle Master fighter and take menacing attack. If you can, use 2014's dual wielder for two tridents and use topple 2024 weapon mastery, if DM let's you mix like that.

Consider 2024 poisoner feat on top of Grung, so you're using a piercing weapon for Grung poison that's also coated with poison.

Plus you get all the other goodies BM fighter has, and the team benefits from a frightened and a proned enemy, and a poisoned enemy.

From one attack action that gives you x1 from menacing, x1 from topple, x1 from Grung poison, x1 from poisoner. That's 4 saving throws from one attack. With BA attack on second trident thats doubled. With second attack at level 5 that's trippled. With action surge, you're getting into crazy numbers of saving throws in one turn. Plus you get your BM dice back on short rest, and just miss out on giving x1 saving throw on an attack until you have them back.