If your DM lets you choose your summons for Conjure Animals, etc, one option is 8 constrictor snakes. They are Large creatures with a CR of 1/4, which means you get 8 of them for a single 3rd level slot. They get an attack with +4 to hit that auto-grapples on-hit, restraining them with a DC14 escape. If there's a lot of mooks to fight in a boss battle, you can use this to get some breathing room and gimp the boss's action economy advantage.
One at a time, have them attempt to constrict a mook of size Huge or smaller, until two snakes are doubled up on one mook, then move on to the next one …