Thanks. If that's the case, can a character shoot another character if they're adjacent to each other through stairs?

Yep, as long as all the other requirements for ranged combat are met (LoF, not adjacent to an opposing character) you can ranged combat someone down stairs. You have the option of using close combat as well if you like, which is why they are pseudo-adjacent.

Can his trait ignore first turn immunity if he can go to the opponent's starting area on the first turn?

First round immunity prevents the characters from being damaged, so no his power will not ignore FRI in any way even if you managed to use it on the first turn.

Please forgive the newbie question, but this trait does not ignore defenses, does it?

Nope, so defense modifiers would still kick in.

That's correct. The damage is not penetrating, unavoidable or in other way ignoring damage reducers so if a hit character can use one it would kick in.

Sorry for the thread necromancy, but would the characters being damaged get to use Super Senses? What about Shape Change?

No. Characters only roll for Shape Change when they're the target of an attack or Super Senses when there is any attack roll.

ok, i'M playing Grammer Nazi now. According to the power (trusting what the OP put) it says damage a character in the square chosen OR adjacent. Not and. So is it supposed to be an AND or do you have to choose?

Hmmmmm. Methinks Magneto and Morphing Jar are gonna be good friends.

It hits any characters in the chosen square and surrounding squares. If the "or" were changed to "and", as written, it would only work on multibase characters.

There's nothing wrong with the grammar. Theres nothing there to suggest that the or is exclusive. It's not an "either or".

mirandir is correct. The logical operator or means "At least one of" the things that it applies to, whereas and means "Every single one of" the things it applies to.

Hooray formal logic.

For those who didn't have to suffer through a fundamentals of logic class in highschool here is the easy way to tell if you satisfy an or, an and, or a causal statement.

A v B is true unless (not)A & (not)B is true

A & B is true IFF A is true and B is true

A -> B is true so long as either B is true, or A is false.

As such with a statement of "In or adjacent" we know that this is going to be true of the questioned character under the following scenarios

1. The character is in the square, but not any adjacent square
2. The character is not in the square, but is in an adjacent square
3. The character is both in the square and an adjacent square.

And will be false only if

4. The character is neither in the square or the adjacent square.