1. Thrall from Warcraft: Sam is not allowed to stand still at any point. Should he stop moving, he will drop dead on the dot. Thrall is peaked in power but has only slightly above human durability.
This one seems straight forward enough to me. If Same puts enough bullets in the Thrall in short enough order, the Thrall dies, and he advances. If he does not, the Thrall makes him dead, and he does not advance. I'm thinking, seeing he can choose the appropriate equipment, he wins.
2. Link from Zelda: Sam is given only his handgun and only nine bullets and seven of those bullets has to hit Link. This is TP Link and he is not allowed speed enhancers. He is allowed to switch between wolf and Link form. If Sam can land seven bullets, Link will be pulled out of the game and Sam moves on.
This one is interesting. Landing seven bullets on Link would not be easy, especially after the first one alerts Link to Sam's position. With Wolf form he has enhanced senses and agility, but in human form he has a shield. In either case, it only takes three misses or blocks for Sam not to advance this round, or one arrow from Link before all seven bullets land. (And Link in TP pegged an inch thick pole at great distance with no assistance to his aim.) Imho, Sam needs to land too many shots with too few bullets. Wolf Link would be very hard to hit, and human Link's shield is very handy. Either one seems to have the option to fight back, potentially killing Sam.
The setting also benefits both of them because it seems that it would have a great deal of cover. But because Sam has only nine bullets, and must land seven, this is more helpful to Link, who could potentially wait Sam out by just sitting behind a corner, forcing Sam to move. With his Wolf Senses he could even keep track of Sam's movement to a degree without seeing him. Link would also be faster, allowing him to remain down wind. In my honest, and probably bias opinion, he cannot land seven bullets with only nine shots. But let's advance Sam anyway for the sake of an interesting thread. I want to think over the other matches.
3. Sephiroth from Final Fantasy: Sephiroth is required to track Sam down and kill him within twenty minutes. Should Sephiroth fail to accomplish this, he will be banished from the battle and Sam is declared winner.
Unless Sephiroth has some sort of hightened awareness, I don't think he could find Sam easily. He is fast enough to check 'hiding places' at great speed, but Sam is good with stealth and camoflauge. I'm not sure how to call this one. If Sam moves, his tracks could prove to be his undoing, thanks to the snow. But with the right equipment, he could simply lay in the snow for twenty minutes. Conversely, Sephiroth does have Tk which he could use to stir up the ruins, and the snow, turning this in his favour.
4. Kain from Legacy of Kain: Given bullets fueled with a magic negating power, Sam is expected to place a bullet in Kain's chest to completely cut him of his magic source. Sam is also given the ability to teleport (Instant). Sam can also use his gun and shoot himself anywhere, turning him completely immune to anything Kain can do against him for five seconds per bullet (Does not stack), this however also disable his own teleport. Kain is aware that the bullet must hit his chest.
I'm not sure about this one either. Instant teleportation is better than Kain's own, and I don't think Kain has the reaction time to handle an instant teleport followed by a bullet. Convesely, Sam may have to shoot himself to avoid blood siphoning, but he might be able to simple teleport out of that, or shot Kain as he attempts it. Imho, Sam, by way of superior teleport.
5. Snake from Metal Gear Solid: Thrown at a random location, Snake is expected to hide from Sam for 24 hours. If Sam can find Snake, he is banished from the field and Sam is declared winner. Snake is unarmed and is disqualified if he picks up anything that can be used as a weapon.
I'm thinking Sam can track Snake, particularly if he's allowed infrared. No box will hide Snake from that. Given that Sam also has 24 hours, and Snake would leave tracks if he moved, Sam wins here.
6. Master Chief from Halo: Master Chief does not get a visor for his helmet, but is other than that his own merry self at both armor and physial fitness. Sam gets the weapons of his choosing and two hours preparation. No further rules.
Sam. The sound made by a sniper rifle would not meet MC's ears until after the bullet had already met his face, thus allowing him no que to react, and Sam's a good shot, allowing him to take this, if he makes it with his first bullet. Which he probably will. So, I say Sam more often than not.