COLOSSAL STAMINA
This character automatically breaks away and can make ranged combat attacks against non-adjacent opposing characters when this character is adjacent to opposing characters. When this character has two action tokens, it can be given a non-free action. If you do, after actions resolve deal it 1 unavoidable damage and do not clear action tokens from it at the end of the turn. This ability can’t be countered.

Can a Colossal character use Multiattack, ignore [insert power name here], break away automatically, or do something else that isn't in the Colossal Stamina or Great Size descriptions?
Maybe. Many Colossal characters come with their own special rules sheets that detail a lot of extra stuff that they can do or ignore or otherwise change the way they might normally work. However, those rules are not common to all Colossal characers and just because Colossal A can use the Multiattack does not mean that Colossals X, Y, and Z can, too.

Basically, if a Colossal does NOT have its own special rules insert, the Colossal Stamina and Great Size ability is all they can do (barring other special powers and abilities, of course).

Can a Colossal character attack opposing characters two squares away with a close combat attack?
No. You are thinking of the Giant Reach ability that character with the symbol possess. While the and symbols are typically given to very large characters, the abilities that those two symbols give to their respective characters are different abilities. Giants can do some things Colossals can't do and Colossals can do some things Giants can't do; just because they are both "big" characters does not mean that they can all do the same things.

Can an Colossal character make a ranged combat attack against an adjacent opposing character?
No. The Colossal Stamina ability does allow a Colossal to make a ranged combat attack against non-adjacent opposing characters if there is an opposing character adjacent to the Colossal, but the adjacent opposing characters can't be attacked with a ranged combat attack.

So what about Pulse Wave then?
Beginning with the 2011 Powers and Ability card, adjacent opposing characters can't prevent any character from using Pulse Wave. Colossals are no exception. Blast away!

Older Colossals, like Galactus and Spectre, could keep pushing and not take any damage... however this new Colossal Size ability says that the Colossals will take unavoidable damage for taking non-free actions more than two turns in a row. What does this mean for those older Colossals?
In cases where older Colossals have a rule that specifically allows them to do something that is not otherwise described in either Colossal Stamina or Great Reach, follow the instructions in the rules inserts.

So, for example, if Galactus' insert says he can keep pushing, and that he does not take pushing damage, that is something not specifically covered by Colossal Stamina (notice the ability description written above says nothing about pushing) and you would follow the instructions in the insert. Galactus can keep pushing, even when he has two tokens, and he does not take pushing damage when he does so.

Edited and changed the Colossal Size entry to reflect the new Colossal Stamina ability.