This isent really a "stage" in a way, well maybe the second example is but it's more how they completely upend the game in a bad way
Monster Hunter World, specifically two fights.
Behemoth, when this released I just instantly went "WTF" essentially they tried to add MMO mechanics to Monster Hunter, phases, enrage mechanics with an instant kill, even a red beam which signifies which player has Agrro, yes they added tanking from MMO's to Monster Hunter. This meant the fight played against the rules of the series up until that point and I hated it, but it was cross over so I put up with it. Sadly this poor idea of MMO raiding would slowly evolve into something much much worse.
Alatreon, essentially they decided to make a boss that unless you did a specific amount of elemental damage per phase he would enrage and one-shot the team... yes more MMO mechanics.
Why did this suck? For people who don't play Monster Hunter certain weapons are better at dealing raw (none elemental damage) or Elemental (well... elemental damage) so if your one of the weapons that sucks with doing elemental damage you where stuck on hard mode for this fight, or you switch out. Worse still things like "Blast element" something literally called "element" did not count meaning even more builds where rendered useless ONLY for this fight. No other Monster has ever demanded you specifically change a load out, you could always compensate with skill, but not for this guy you had to play elemental or go home.
Both of these fights drastically changed how you had to play Monster Hunter World, by introducing mechanics that they demanded you deal with and if not would one-shot the group, failing the hunt. This is not what people play Monster Hunter for and it pleased me immensely that none of this shit made it into Rise.