lvl 1: the plural of octopus is octopuses because the plural version of a word is the word with an s at the end
lvl 2: the plural version of octopus is octopi because if a word ends with "us" the plural version replaces the "us" with "i" e.g. cactus -> cacti and fungus -> fungi
lvl 3: actually, that rule is only for latin words. octopus is a greek word and the correct plural is octopuses or octopodes
lvl 4: actually, language is descriptive not prescriptive. since enough people over time have used octopi as the plural for octopus, it's a valid plural
lvl 5: the plural of octopus is octopeese, like geese
