Quest 3 from original quest broken for heroes?

By Crycious, in Descent: Journeys in the Dark

we are currently playing quest 3, In it the end boss is a namd naga that canted be attacked by normal attacks. The naga is blocking the last bell we have to activate to win the quest. Since we cannot target the naga it is at a stalemate. It wont move and so we can't get around it. Basically now we would just sit there until the overlord goes through the deck anough to get rid of our conquest tokens. Can we move through the naga? or can we activate the last bell in some other way? It also says the naga has to end its movement adjacent to the rubble. We understood this to mean diagonaly from the rubble counts as well. Is that incorrect?

Diagonal is adjacent, but I seem to recall that room was very carefully laid out so that the boss can't get anywhere that will block the heroes. The rubble's too close to the back wall for the naga to get around to the back and block the corridor leading to the middle bell, and it doesn't extend far enough north or south for the naga to actually get into the north or south corridors and block those bells.

Remember that the boss does NOT have the Grapple ability, and that heroes can move diagonally between a monster and a wall (as shown in the diagram on page 9 of the rules).

I don't have the quest 3 map in front of me, so it's possible I'm forgetting some crucial detail, but trying to use the boss to block access to a bell was my first thought when I read the quest, and I definitely concluded at the time that it was impossible.

The naga cannot end on the rubble only adjacent to it so the heros CAN get round the back or either side to get the last bell.

also remember the naga cannot move over the rubble to go behind the rubble to block the corridor.

Our group played this about 2 months ago(me as overlord). I recall I was thinking of using the naga to block the path to the "last" questionmarker, but realized it would be impossible. As others say, the master naga doesnt have grapple, and also it cannot walk through the rubble. Since it also has to stay adjacent to the rubble marker it cannot be used to block the entire hallway

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N = naga

E = empty space

R = rubble

When the area is revealed there are also two additional normal nagas, they are not marked here since they can be killed as per normal rules.