What actions can an OL have his monsters do each round.

 Only one attack action per monster

but he may then perform any other action that is not an attack 

So by my understanding the master ettin can attack, and throw if he wants 

Elementals may attack and either use Earth, Air(which has been nerfed), or water. But not attack and use fire, because it says perform an attack

The master flesh moulder may heal and attack, etc….

Obviously they may choose to move too in addition to any other action. 

Two actions per monster.

No more than one attack action.

Other actions can be accomplished twice.

OL cards can trump those general rules.

Robin said:

Just to seek clarification on this point - is this they cannot make two attacks, or cannot take two actions that are considered 'attack actions'.  There are many creatures that have a listed action that says something like 'Make an attack that does X'.  Does this count as their attack for the turn?  And if not, they would be free to do this twice, surely?

FYI, we were playing last night and a giant did a double sweep on us because it wasn't an 'attack' (it was a sweep).  Was that wrong?

I believe that if an action description contains the word "attack", it counts as an attack action.  It has been suggested that if it requires you to roll the blue "attack" die, it is an attack action.  If the action does not meet either of these criteria, I guess it can be used twice.