Use your ultimate to keep people away, the optimal time to use it is overtime on center.
in case of pushing the payload, you can put it in front of the cart.
Make sure either Grohk or his totem is dead before using your ultimate. Give about a second after the totem dies, so that the enemies' CC immunity wears off first. Otherwise, your Ultimate will do nothing when the enemies have CC immunity.
Make sure you have scamper available before using Moji's ultimate or else the enemy might escape after you transform them into a treat as without scamper its really hard to finish the treat especially if the enemy is constantly jumping.