Have a look at the situation below. Is this correct?

Hellhound is first on the left hand side. It costs 2MP to move one forward, now in the tree so has shadowcloak (even though his ass is sticking out the back).

His next move is out of the trees diagonally, so he only pays 1MP.

Then the tricky bit. His next move is diagonal, his front half not in the trees, so paying only 1MP, but his back half is in the trees, so he gets the shadowcloak?

Since part of him is moving into a tree space, he's going to have to pay 2MP to move to that location, it doesn't matter for movement that its his back half. If any part of the monsters base enters a tree space it has to pay the movement to do so.

And he will gain the benefit from Shadowcloak, as per the FAQ:

A figure receives the benefits of a terrain feature if any part of its base is on that terrain feature. For example, if half of a spider’s base is on a table, the spider is considered to be elevated.

Big Remy said:

Actually, per the paragraph above the one you quoted in the FAQ:

When a large monster moves, it suffers the negative
effects only of whatever terrain its “front” half enters. For
example, if a spider were to move from four clear squares
to a mud square, it would suffer a movement penalty.
If that same spider were to then move its “front” (i.e.
leading) half off the mud into clear terrain, it would not
suffer a movement penalty even though its “back” (i.e.
trailing) half has just moved onto the mud

So it will only cost 1 mp. My group has house ruled this to instead make it only cost extra movement when a monster moves onto a space that none of it occupied, which makes more sense.

I read that rule different, and here's my reasoning. Which may or may not make any sense

The Hellhound moved from a clear space ( the two below the trees) and into one that has an obstacle with a movement penalty, the tree. The whole front half/back half thing shouldn't apply here, because that should only deal with situations where the monster started its turn inside an obstacle with a movement penalty, as per the example you quoted.

Look at the sentence: When a large monster moves, it suffers the negative effects only of whatever terrain its “front” half enters. For example, if a spider were to move from four clear squares to a mud square, it would suffer a movement penalty.

That is exactly what is happening here, except its a tree instead of a mud space. To me, the whole front/back half issue is ambigious at best since monsters have 360 of LOS. Otherwise, Hellhounds would be restricted to using the breathe template from their mouth and would have to spend MP to turn around to hit the Hero behind them.

From my reading of the rules, the Hellhound would have to spend 2MP to move there and it gets Shadowcloak. If it cost 1MP, that implies it is not entering the space with the tree which it clearly is. If people rule that it only costs 1MP to enter that space, then the Hellhound should not get Shadowcloak as well for free basically.

Otherwise, it creates a giant loophole where large monsters can essentially "back into" beneficial terrain like trees, tables and the like without having to spend the 2MP to gain the benefit.

Just my take on it.

Indeed, that makes a lot more sence since many large monsters don't really have a facing given their round base...

Big Remy said:

Thats a good way of looking at it. The whole front half/back half thing was put in there to stop large creatures suffering the negative affects of things twice as much as small things.

I would say that the hellhound should have paid 2MP because both of its spaces were in clear terrain before and moving to somewhere that at least one of its spaces has a penalty.

Yeah, I mean the fact that "front" and "back" appear in quotes leads me to believe that they are merely being used to describe the location of the model in relation to the given terrain obstacle.