Cactus - Cacti Sarcophagus - Sarcophagi Octopus - Octopi Campus - Campi Mouse - Mice House - Hice
I know this is a tongue-in-cheek comment, but octopuses is generally preferred: https://oceanconservancy.org/blog/2022/02/01/plural-octopus/
Before using wrong a plural in a language you don't know, just use an anglized plural, octopuses (or octopusses).
Afaik, octopodi would be correct as 'pus is actually derived from ancient greek "pous" meaning foot (latin would be "pes"). And even in Latin, not everything ending on -us has -i as plural.
