Basically ever MMO that shuts down is the obvious answer, some games have dlc that's no longer available but the biggest examples I have are Pokémon ones.
In fire red/leaf green and emerald there's islands with Pokemon normally extremely rare that people had very limited time to unlock, emerald has one for mew with a little lore attached that never made its way to the west despite being fully translated, I recently found a way to unlock these since it felt wrong that part of the game was locked away despite at some point being intended to be seen (the mew one most of all since they decided to give a way a mew instead of the old sea map.
Gen 4 has loads of these events, famously arceus was never catchable because game freak was concerned it was too hard to find, and of course now the ones that were are lost to time, hgss has the celebi time travel event that requires a special celebi event and is the only way to fight the OG team rocket boss in the game and learn about his connection to the rival of gen 2 in game.
Gen 5 has a couple of things but mostly nothing too large, and that's basically it until recently with the gen 4 remakes, their Evers are almost impossible to get now too despite being less than a year old.
If anyone has any other examples of these or wishes to discuss any I'm most interested, personally I find it quite a sad concept, losing a part of a game to time, I'd rather stuff like the events above just be password restricted so that they never expire.
In fire red/leaf green and emerald there's islands with Pokemon normally extremely rare that people had very limited time to unlock, emerald has one for mew with a little lore attached that never made its way to the west despite being fully translated, I recently found a way to unlock these since it felt wrong that part of the game was locked away despite at some point being intended to be seen (the mew one most of all since they decided to give a way a mew instead of the old sea map.
Gen 4 has loads of these events, famously arceus was never catchable because game freak was concerned it was too hard to find, and of course now the ones that were are lost to time, hgss has the celebi time travel event that requires a special celebi event and is the only way to fight the OG team rocket boss in the game and learn about his connection to the rival of gen 2 in game.
Gen 5 has a couple of things but mostly nothing too large, and that's basically it until recently with the gen 4 remakes, their Evers are almost impossible to get now too despite being less than a year old.
If anyone has any other examples of these or wishes to discuss any I'm most interested, personally I find it quite a sad concept, losing a part of a game to time, I'd rather stuff like the events above just be password restricted so that they never expire.
