Is line of fire blocked between a character and a wall at a diagonal?
Ex:

C = character W = wall -- = clear terrain

C--
--W

The rulebook doesn't state how a character and wall interact at a diagonal and someone this weekend was shooting through the diagonal.

Someone was cheating.

. . .|. . .
. . .|. 2 .
. . .|. . .
. . . A . .
. 1 . . . .
. . . . . .
LoF is blocked from 1 to 2.

Is it because walls count as blocking terrain for LoF?

Yes.

In this case, both squares block LoF, so the intersection is the least restictive of those...blocked.

Thanks. Rep to you.

also, if H is hindering terrain, then the hindering terrain modifier would apply for line of fire from 1 to 2.

. . .|. . .
. . .|. 2 .
. . .|. . .
. . . H . .
. 1 . . . .
. . . . . .

How does this scenario work for movement purposes? Can a character move diagonally between a character and a wall? Or in the last scenario, will the character have to stop after it crosses the hindering marker?

first scenario "between the character and the wall" it depends.
If the character next to the wall is friendly to the fig that is moving then go ahead its free for movement.

If the character next to the wall is an opposing character, then it depends on the moving fig, if it has an ability that allows him to ignore opposing figs on movement there will be no problem, if the fig does not posses such ability then it will stop before crossing the intersection.

second scenario "between hindering terrain and the wall" you pick the lest restrictive type of terrain and apply it, in this case will be the intersection between blocking and hindering so you consider it hindering, that way your character has to stop after you cross the intersection, unless your fig has an ability that allows him to ignore the effects of hindering terrain on movement.

One technical adjustment...most characters no do not ignore other characters for movement. Rather, they can move through squares adjacent to and occupied by opposing characters. This has no effect on this scenario, but it does matter for the Kingdom Come/Hypertime team ability.

I think I understand your point but I really can´t understand the first part of your post.

But if you want to correct me regarding the exceptions I suggest you go the whole way and explain all the exceptions to what I said :D

This was just a technical adjustment, not an exception. The focus in the technical adjustment (and it really was just that) was to the term "ignore opposing characters for movement." Ignoring characters on movement now actually means something in Heroclix. While characters that can use Flight or Leap/Climb can move through squares adjacent to and occupied by opposing characters, a character that "ignores" can do all that PLUS they can do other things like ignore the Kingdom Come/Hypertime ability. (There may be other cute tricks too.) Right now, only two characters do this -- Kid Flash and Dying Barry Allen Flash. But since it now has meaning, I figured I would mention it.