Team Ninja's upcoming Souls-like Wo Long: Fallen Dynasty is taking another note out of FromSoftware's book with enemies that summon real players to fight you. If you're playing online, be ready for a duel that may be the easiest fight in the game, or too gruelling to manage.
Producer Masaki Yamagiwa revealed this mechanic in an interview with NextGen Player (thanks, mp1st), "There will be PvP in the game, for example, a player or NPC coming into your world is one way we do that. You can go to other players' worlds as well to fight in PvP. Also, there will be areas you can place a flag... there will be an enemy there and that enemy may be able to bring in regular NPC enemies or other players - and then you can decide, do I want to fight the player first or do I want to fight the big enemy? And if I beat the big enemy then everyone goes away. So you can decide what to do in that regard."
It sounds a lot like Demon's Souls' Old Monk and Dark Souls 2's Looking Glass Knight - the former would either be an NPC boss fight like any other, or it would be an invader specifically summoned to take the boss' place. They would even have a big beefy health bar. As for the Looking Glass Knight, they could summon black phantoms via their mirror shield to fight alongside them, either inviting real players or NPC fighters. If you defeated the Looking Glass Knight, the phantoms would vanish too, a lot like Wo Long: Fallen Dynasty's mechanic.
Wo Long: Fallen Dynasty is building on Team Ninja's work with Nioh and Nioh 2, building on the first game's PvP mode. Not only will there be a functioning PvP portion, but certain enemies will be able to gank you with real players - luckily, this seems limited to specific areas, so not every enemy has the capability to double-team you.
But on the other hand, that should make for a fun way to pass the time when you're struggling with an area - you can always hop into someone else's game and have fun playing the role of an enemy instead.