Two is more than one.
Blizzard has updated the a bunch of post-patch list of Diablo 3 PTR Known Issues, and they range from minor to hilariously dangerous. The best one is the game now spawning one Greater Rift Guardian for every player in the game, if you fail to clear the rift before the timer expires. (That’ll teach you to be slow!) Here’s the full list as of Wednesday afternoon.
CombatWizard – All rune variants of Hydra are dealing 100% weapon damage instead of their listed damageDemon Hunter – Attacks made by Sentries against enemies with a Reflects Damage effect will be reflected back onto the Demon Hunter.
Greater RiftsFailing a Greater Rift timer within a multiplayer game will cause a Rift Guardian to spawn for each member of the partyNote: This can additionally occur in a single-player game by reaching 15 minute mark as you are just about to complete the rift, and then gaining enough progress to complete the rift at the same time as or just after the Guardian spawns.Gem selection remains disabled in Urshi‘s gem upgrade UI after you attempt to upgrade your first gem, even if additional upgrade attempts are available
ItemsTorment-Only legendary items do not drop from Greater Rift Guardians if the game difficulty is set below Torment IHand Crossbows were given an unintended increase in damage in this patchKilling elites too quickly may cause tje Bane of the Powerful legendary gem to fail to proc
Double GRGs can even appear in a single player game, if you do it just right.
Two Guardians spawned at the end of a Greater Rift
I was doing a level 30 Greater Rift. I failed to summon the boss before the time ran out, by about 2 seconds at most. (It was very close.) I was fighting an elite pack when The Binder spawned. While fighting the spider, I ran around to a better position. When I picked up the purple globes from the elite pack I’d been fighting, a second Guardian spawned, Saxtris.
Tsarnis: Thanks for the reports about this. We are indeed aware of the issue, and as other players have mention this is in our known issues list. I went ahead and edited the entry in known issues to indicate that this can also occur in single player games under certain circumstances.
It’s not all bad, since all of the GRGs drop just like normal, so in a four player game you could be looking at 6-8 legendary items when (if) you survive the battle. Some funny footage of the mad scramble created by four GRGs appearing at once can be seen courtesy of Twitch streamer and King Leonidas cosplayer MICHAEL13785.