Ok so I have to ask for a clarification as for how Grease Trap works in a particular situation.

"Play this card when a hero enters an empty space from an adjacent space. He tests Awareness. If he passes, he suffers 1 Fatigue . If he fails, move the hero 3 spaces in a straight line in the same direction he last moved. For each space he cannot move, he suffers 1 Heart or 1 Fatigue (your choice).

Mage: If he fails, the hero is also Stunned."

Now if the hero decides to use fatigue to move to contact in order to attack twice. I should be able to trap the hero during the forced move with Grease Trap, which is where I would think I could inflict him 3 damage since he has 0 move points at this point and can therefore not move the 3 extra spaces. But my heroes argue that the hero has two actions left and could use a move action to get these move points back into the pool and therefore would not suffer any damage. What do you think?

I always interpreted grease trap to mean they take damage or fatigue if their forced movement would push them into an obstacle or wall or something where they cannot legally enter, not that it costs them movement points. No other forced movement in the game uses movement points, so whether he has movement points or not is irrelevant, as that doesn't prevent forced movement from grease trap.

That said, if it were interpreted the way you say, you would be correct: actions must be declared ahead of time, you cannot interrupt the effects of an overlord card to declare an action. He did not have the movement points at the time of the card being played, he cannot spontaneously react by spending an action: currently active effects must resolve first. If there was a timing issue with two effects resolving at the same time he'd be in the right, but the grease trap clearly resolves first.

Regardless, the forced movement from grease trap does not use movement points.

Wow. I guess the wall/obstacle situation has never presented itself yet, so my interpretation was indeed that the hero was forced to spend movement points to cover the extra 3 spaces from the Grease Trap, otherwise he/she would be suffering 1 damage/fatigue per space he cannot move to (due to lack of move points).

I can definitely understand your version, though. I can see myself doing it your way in the future. My interpretation seemed legitimate at the time but yours made it overcomplicated and less likely to be true.

Grease trap is nothing about movement points, but more a forced move. So, in your example, the hero cannot do anything but suffers fatigue or damage, since the hero can't do something while you play your card and it is resolved.

Let us have an example :

a hero declare a move action and moves 1 spaces (his speed is 4), you play grease trap, he fails, so you move him 3 spaces, and then he have 3 more movement points left to do whatever he wants to.

Imagine you slide on a banana, you slide, but you can still move and go where you were wishing for.

Ok so I have to ask for a clarification as for how Grease Trap works in a particular situation.

"Play this card when a hero enters an empty space from an adjacent space. He tests Awareness. If he passes, he suffers 1 Fatigue . If he fails, move the hero 3 spaces in a straight line in the same direction he last moved. For each space he cannot move, he suffers 1 Heart or 1 Fatigue (your choice).

Mage: If he fails, the hero is also Stunned."

Now if the hero decides to use fatigue to move to contact in order to attack twice. I should be able to trap the hero during the forced move with Grease Trap, which is where I would think I could inflict him 3 damage since he has 0 move points at this point and can therefore not move the 3 extra spaces. But my heroes argue that the hero has two actions left and could use a move action to get these move points back into the pool and therefore would not suffer any damage. What do you think?

The key is in what I bolded. It's exactly like Whitewing and rugal said. You slip on a banana, and slide into a wall, taking damage for all the extra momentum you still carry. Try to Grease Trap your hero's as they finish their move adjacent to your monsters, when they are near wall, or for extra fun, when they are near a large pit or lava (They'll take the fall damage or burn damage).

Indeed- I used Basic 2 recently, and by the end of the campaign, the heroes were very careful about the directions they moved with each space, trying to ensure that if they got Grease Trapped, they wouldn't take damage. However, I always save the card for a mage for the free stun.

One time, the OL in our group played it but he had miscounted the range to the wall. It actually helped the heroes, by giving the activating hero an extra 3 move forward, to get in range of the monsters.

So play this with care and forethought!