WHO WOULD WIN IN A FIGHT BETWEEN THE DOVAHKIIN, THE CHOSEN UNDEAD, AND THE FATELESS ONE.
The Dovahkiin is not allowed to use any armor/weapons he crafts, due to possible exploitation of the smithing system in Skyrim.
The Dovahkiin also does not have a Skyrim-esque sneaking ability, seeing as it is utterly overpowered and broken without the use of a realism mod.
The Fateless One cannot go into the fight with a full Reckoning meter (ala DMC's Devil Trigger for those of you who haven't played KoA:R), due to Reckoning mode being horrendously overpowered in a fair fight. If the fight lasts long enough for the Fateless One to gain a full Reckoning meter, then it's fair game to use it.
The Chosen Undead cannot use the Dragon Head Stone soul glitch to easily get to max soul level.
Since the Chosen Undead cannot pause a fight to use Estus Flasks (potions) or change his armor and weapons, the Fateless One and the Dovahkiin cannot pause the battle to use a potion or change equipment, as they would gain a clear advantage. Anyone can switch equipment or use a healing item mid-fight, however it takes up to three seconds of standing still to change equipment and the small amount of time it takes to drink an estus flask to use a healing item (I decided on three seconds after doing a "how fast can I equip random pieces of equiment" test on my Dark Souls save, and three seconds was my average time).
The battle will take place in an Imperial gladiatorial arena in bright daylight, to prevent any unfair use of sneaking abilities.
The Dovahkiin is allowed to bring Lydia, with all the burdens she can carry.
The Chosen Undead is allowed to summon Knight Solaire for some jolly cooperation.
The Fateless One is allowed to bring his Fateweaver mentor Agarth to let him relive his glory days.
Predicted Advantages/Disadvantages for each Character:
The Dovahkiin can go invisible with the use of your standard illusion spell, the other two would be at an extreme disadvantage.
Not if the Chosen Undead had prepared for this by equipping the Fog Ring, which allows him to detect invisible enemies. The Fateless one can also spec into Detect Hidden, which detects enemies and hidden treasure.
The Fateless One is at a huge advantage do his acrobatic abilities, like the ability to roll and blink short distances.
The Chosen Undead has the ability to roll, albeit slower, but can quickly equip the Dark Woodgrain Ring for extra mobility via rolling. The Dovahkiin is at an extreme disadvantage in this aspect, due to not having the ability to roll or dodge.
The Chosen Undead can wear extremely heavy suits of armor, such as Havel's set and the Stone Armor, blocking nearly all damage from minor attacks. Could he not just tank all the attacks from the Dovahkiin and the Fateless one?
Yes, but the Chosen Undead becomes extremely slow when wearing these heavy suits of armor, leaving him open to the quicker Dovahkiin and Fateless One.
How would the Dovahkiin deal with the Fateless One and the Chosen Undead having the ability to parry blows, since he cannot?
The Dovahkiin can literally stand in one place with his shield up and take as many hits as he wants, unlike the Chosen Undead and the Fateless One, who are pushed back or knocked over after being hit too hard while blocking. The Dovahkiin can also shield bash to block a power attack, and although it isn't a proper riposte or parry, it gets the job done.
The magic systems in each game vary, how would a magical dual between the three work out?
Each character has their own magic system intact, nothing is standardized, except the Chosen Undead receives a mana bar to make things fair.
Do I even need to bring up "Fus Ro Dah"?
Fus Ro Dah is overpowered in Skyrim because no one can roll out of the way. The Chosen Undead and the Fateless one can both do combat rolls, so it's their own fault if they get caught in the middle of the shout. The Chosen Undead can also subvert Fus Ro Rah by having enough Poise to stand up after being hit.
What about the Dovahkiin's ability to summon Odahviing?
It's fair. Both Fateless One and Chosen Undead have fought and bested dragons, and since Odahviing and every other dragon in Skyrim are largely simple to defeat in combat they'll probably have no trouble dealing with him. If the Chosen Undead chops of Odahviing's tail he might even find a dragonbone weapon.
Is the Chosen Undead allowed to chain backstabs?
It's a combatant's own fault if he gets backstabbed, so yes, Chosen Undead can backstab all he wants.
The Dovahkiin can summon a daedra reinforcement, and the Fateless one can summon a Fae Gora, doesn't this put the Chosen Undead at a disadvantage?
Since the help summoned by the Dovahkiin and the Fateless One are relatively weak, the Chosen Undead can summon Maneater Mildred if he becomes outnumbered.
Do the Dovahkiin and Chosen Undead get unlimited arrows, since the Fateless One has an unlimited supply of projectiles?
Purely for balance, each warrior has a one hundred arrow limit. The Chosen Undead only receives ten arrows if he uses the Dragonslayer Bow.
And for balance's sake, maximum health and damaged dealt is roughly standardized between the three characters. A power attack from a Daedric Greatsword, a +5 Black Knight Greatsword, and a top tier crafted blade forged by the Fateless One all do roughly the same amount of damage.
WHO WINS?It's hard to predict who would win this kind of fight, although a rough consensus among a council of five has came to the conclusion that the Chosen Undead wins the battle. Although the Dovahkiin is a powerful warrior, his tendency to swing his weapon with reckless abandon may tire him out and open him for a parry, which the Fateless One and the Chosen Undead would be happy to tend to. However, damage caused by the large stable of magical moves and shouts from the Dovahkiin would leave the two remaining combatants weakened. The Chosen Undead would rise to the occasion and slay the Fateless One, due to his extreme ability to bounce back when he is pushed down. The Fateless One is nothing compared to Ornstein and Smough, Gray Wolf Sif, or Gravelord Nito, and he goes down hard, but still fighting. It is the iron will and sheer ability as a warrior of the Chosen Undead that wins him the fight.
In regards to the companions they can bring with them, it would be a different outcome. Agarth's ability to see into the future is destroyed by the Fateless One taking part in the battle, so he is at a loss with his ability. He would likely go down after an arduous fight, seeing as he deals a little amount of damage but can tank an extreme amount of damage before falling in battle. Knight Solair and Lydia, being seasoned warriors, are evenly matched, and we were unable to come to a consensus as to who would win in single combat. But since the Chosen Undead would likely survive the fight between the protagonists, he would likely come to Solaire's aid, saving him from death by the Nord warrior's hand.
HOWEVER: If the Fateless One defeats enough foes to gain a full Reckoning Mode bar, which is extremely circumstantial due to the need to kill multiple hostiles to fill the bar (if it happens, blame the Dovahkiin for continuing to summon daedric help), he wins the fight hands down due to the sheer power he gains in Reckoning Mode. Like I said though, this is extremely circumstantial and unlikely to happen.
CONGRATULATIONS, CHOSEN UNDEAD.
In conclusion, how hyped are you for Prepare to Die Edition?