Magnetic Field: Magneto can use Energy Shield/Deflection. When Magneto uses the Carry ability, he can carry up to 4 characters. Modify Magneto's combat values by +1 if he's occupying a square that contains a debris marker.

Magnetic Mastery: Give Magneto a power action. Magneto can use Telekinesis twice as a free action. If Magneto uses Telekinesis option 3, increase the damage dealt by 2.

Magnetic Shield: Magneto can use Toughness. Characters halve their range values when Magneto is one of the targets of their attack.

What exactly is a debris marker? Is that another way of saying "hindering terrain"?
Yes and no. A debris marker is a specific kind of hindering terrain that is typically placed on the map when a wall or square of blocking terrain is destroyed. Some other less common game effects can also place debris tokens. And debris tokens are indeed hindering terrain (the hinder movement and line of fire), but not all squares of hindering terrain are debris tokens. So Magneto will only increase his combat values if he is occupying a square of debris specifically, and not just any old square of hindering terrain.

What does that "Option 3" thing mean in the Magnetic Mastery special power?
Older PACs described the various effects of Telekinesis as options 1, 2, or 3. When you used the power, you pick which option you wished to use; in Magneto's case, if he picked option 3 he would get an extra bonus to the effect.

Translating to the current PAC description of Telekinesis is relatively easy. Any reference to an "option" of Telekinesis is resolved as follows. Option 1: A is an opposing character; Option 2: A is a friendly character or A is an object placed with no attack; Option 3: A is an object placed to make an attack. So in Magneto's case, the A referred to in the Telekinesis description must be an object token and he must use it to attack an opposing character in B. (10-12-11, normalview)

Magnetic Shield causes the range value of a charater targeting Magneto with an attack. What happens if that attacking character attacks both Magento and another target with the same attack?
If Magneto is the target of the attack, the range value is halved. Doesn't matter how many other targets the attacker was planning on attacking. And if this means that the other target is no longer within range (say, the range value becomes 4 and the second target was 5 squares away), then that character can't be attacked.

Please note, though, that this halving is a replacement value and because of Replace Then Modify, it is totally possible to squeeze some extra range out of an attack targeting Magneto. For example, that same character that had its range halved to a 4 is also standing adjacent to 3 SHIELD characters. Using the free action aspect of the SHIELD TA, that range value will now be modified to a 7 total value.

Will Magnetic Shield halve the range of Outwit or PC?
No. For one, that part of Magnetic Shield will only activate if Magneto is the target of an attack; Outwit, PC, and the like are not attacks. For two, Magnetic Shield causes range VALUES to be halved and range values are those little numbers next to the symbol on the dial. Any game effect that has a range, but does not utilize the range value (like using TK or Super Strength to attack with objects at range) will not be halved.

Edited to reflect changes in Telekinesis wording.