Plankton appears on a sign in the Dining Area, which tells customers to buy Chum and Krabby Patties. He may have the same appearance as he does in the cartoon.
Plankton may be The Superior. Evidence supporting this is that neither of them actually make any real appearances.
The Business Official mentions The Superior on Night 1, which means he was hired by The Superior. He is mentioned again on Night 3, about how he thinks Mr. Krabs is a "back-stabbing traitor", giving a little more proof that the Superior may be Plankton. If this is true, then he is referring to the events that took place in the episode "Friend or Foe".
In the show, Plankton is a small green creature, about the size of a jelly bean, who only wants to make Mr. Krabs a failure in business, make his restaurant the greatest in the world, and then take over said world.