system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragonball Z] Who all has canonically seen all three of Cell's forms?

Mainly referring to Cell's "Imperfect", "Semi-Perfect", and "Perfect" forms, as no-one has really seen him outside of those three forms, save for the test tube.
gpt
In person, Piccolo, Krillin and Trunks. Piccolo saw each of them in order. Trunks saw the Imperfect form last when he traveled back to his future. Trunks and Krillin even saw the larval form, when they went back to Gero's lab to wreck up the place.