How is Taven okay in the Netherrealm? Only evil mortals can go there without suffering.
Perhaps it is because he is a demigod. Raiden in Mortal Kombat 9 was able to go to the Netherrealm and back without any difficulty when he unsuccessfully tried to to make Quan Chi an offer of his and other fighter's souls to change sides against Shao Kahn unaware that the Emperor of Outworld and the Necromancer had already made an arrangement of their own. Though there is another question that should also be asked: Why is there an obelisk in the Netherrealm?
This bit of Fridge Logic is furthered with the events of Mortal Kombat X: so far Johnny Cage, Sonya Blade, Jax and Kenshi were able to venture into the Netherrealm and escape alive. Perhaps they were infused with Raiden's power?
The Netherrealm can house any being for a very short amount of time with no ill effects, but those who are tainted with evil can stay without corruption overtaking them. This is actually demonstrated on different accounts. In Mortal Kombat Mythologies: Sub-Zero Sub-Zero was able to go to the Netherrealm in chase of Quan Chi after the latter entered the Temple of Elements and snagged Shinnok's amulet moments after Sub-Zero defeated the last God. Sub-Zero wasn't by any means evil at all, neither was the Lin Kuei, it was merely what they did that left a taint on his soul. Quan Chi even explains this before Sub-Zero fights him. He tells him that he could not exist here unless his soul was tainted with evil. After escaping with Shinnok's amulet and returning to Raiden, Raiden confirms what Quan Chi said was true, but that it could only be changed with himself. Taken a step further, with Shujinko in Mortal Kombat: Deception the first time he enters the Netherrealm after his affiliation with the Lin Kuei. He is able to return a second time even with his soul cleansed by Nightwolf, as well. Which leads to a bit of a contradiction, if you consider Ashrah. Her sword, the Kriss, supposedly purifies her soul with each demon slain. She claims that if she was purified completely, the Realm would spit her out. In that case, either Shujinko wasn't completely cleansed, or Ashrah was blindsided by whoever gave her the sword, my thoughts on the latter. Even Divine Beings, who are often implied to be pure, should be cast out, as they do have a soul regardless of their God-Like status, but they can step foot there with no harm. The realm itself is a natural corrupting force, given its denizens, so over time truly pure beings would succumb and slowly turn into something terrible after a prolonged time. Of course, to the first troper, Taven DID spend a grand amount of his quest before that moment randomly popping heads of mooks like they were dandelions, that's not anything remotely rainbows and sunshine, no matter life or death. Given that knowledge, however, it's not a stretch to imagine that Johnny, Sonya, Jax and Kenshi are able to endure, especially if you take into consideration the lot of them have committed some acts that could be considered evil, even though their intentions are ultimately good.
Although the Kreate-A-Fatality is one of the most criticized things about this game, there is some Fridge Brilliance involved here. The other games were, more or less, formal tournaments, and even those that weren't were bouts between kombatants. Armageddon is different. Here, it's a chaotic free for all. Would the warriors really have time to perform elaborate fatalities on each other on the field, or would they just settle for hacking at each other until somebody dies? In the case of the latter, that's what the Kreate-A-Fatality seems to be simulating.
It's pretty much established that Shao Kahn wins, but remember that part of the story where Shang Tsung claims that everyone who pledged allegiance to him will return from the dead to continue serving him? And now that the Forces of Light are killed off....
In his bio for Mortal Kombat: Armageddon, it's revealed that Shao Khan can revive allies of his who had once sworn allegiance to him, and if he died, so do they. Now, let's list all of the characters who had allied themselves with him: Kintaro, Motaro, Goro, Shang Tsung, Baraka, Reptile, Reiko, Mileena, Kitana, Sindel, Jade, Kano...
Is it sad that I immediately yelled out "MOORTAAL KOOMBAAT!" after finishing that list of names?
Also, in that same game, it's revealed by Fujin that, when a god is destroyed, they're revived as a "blank state", forgetting all of their past life in the process. Note that this is not what happened to Raiden after his attempt to take Onaga with him at the beginning ofDeception. So, what happened? According to Epileptic Trees, he was corrupted by Onaga in the attempt.