I'm pretty sure I've got this figured out, but to clarify


Giants must stop one square away from other figures, and Vice Versa. This is only overcome by Hovering characters and leap&climb/phasing, right?

If either character wants to move closer, they have to roll break away. The Giant succeeds 3-6, and the normal character succeeds on a 5-6, right?

Giants LoF is blocked only by elevated terrain, and outdoor blocking terrain, but Hindering terrain still effects their DV (ridiculous that an engine block adds to his defense, but Wolverine in the way is totally cool)

Everything stated is basically correct, except:

Characters break away from Giants normally (4-6).

Also, any power that allows a character to ignore opposing characters (by either moving past them or through them) renders them "immune" to the Giant's ability to stop movement. Off the top of my head, this would also include a non-flier's HSS option 1 or the Transporter Move/Attack. For example, both Lockjaw and Johnny Quick can run right up to a Giant using those abilities.

Why is it so complicated? Why didn't they just make it the same as plasticity for the break away where it effects both? so dumb.

Also, if someone tries to pounce a giant, they'll stop one square out, right? and they'd still take the damage?

Unless the pouncer is another giant (which apparently negates the +1 damage from the pounce) or a flier, they're unable to get close enough to make a close combat attack against the giant. This is because they have to stop 2 panels away, and close combat distance for regular sized figures it 1 square.

My little brother put Pounce and Vendetta on Sin Venom, and tried to First Strike my Ult Hulk last night

Man was he pissed when I told him he couldn't lol

I think the only way to do it is to "sneak" up on the Giant by using blocking elevated terrain where the Giant can't draw an imaginary LoF out 2 squares.

G
BX
BY

A non-flier Pouncer/Charger could move into X from Y without stopping at Y because the (G)iant's imaginary LoF to Y is blocked by the (B)locking (or elevated) terrain.

Some feats, like Movethrough or Sneak, also allow figures to ignore the Giant's extended adjacency when moving.

Umm... it isn't complicated. Giant's always breakaway on a 3-6; standard characters on a 4-6.

The only way it gets "complicated" is if stuff like Plasticity or Slippery start getting in the mix. Now you've got to remember who has what power/feat and if/how it effects interactions with other characters.