Dynasty Warriors 8 Empires is probably one of the most outright time-consuming ones I managed. It's not exactly a game of skill but the platinum is rare in part to the fact that you need to commit minimum ~20 playthroughs and earning every single "Title" in the game, a special designation given when you complete a set of goals, stuff that wasn't clarified until other players online listed the exact requirements, and many of the titles are on shared tiers, where you can never earn a new title on an equal or lesser tier than the one you're currently at. Many of the endgame ones require multiple missions of a certain type, dozens of invasions or defense battles, or a long amount of time passed in-game. Most musou games have a tedious platinum but that one stood out to me, much less engaging than the likes of Samurai Warriors 4.
There was also a thing for having 3 concurrent invasions to your territory at the same time and that felt completely luck based, brute-forcing that into happening took more time than I would've thought.
