In Super Mario Sunshine, it is possible for many NPCs that are not usually supposed to sink into goop to actually be made to sink into goop during regular gameplay. Whenever Mario passes through goop, he leaves a small trail of it after himself. The trail can be accumulated as passing through it lets Mario extend it by a few more steps, allowing Mario to (very slowly) take the goop nearly anywhere on the map by doing it repeatedly.
As such, NPCs normally standing outside of goop can be made to sink into it by having Mario bring the goop to them. They all have animations for sinking into goop, even if those would not normally be seen.
However, despite having an animation for sinking into goop, as seen above, Toadsworth is actually coded to be completely immune to goop. Unlike the majority of NPCs, no matter how much goop is around Toadsworth, he will never sink into it, making the above animation entirely unused.
Main Blog | Twitter | Patreon | Small Findings | Source