So the great blood-magic Macguffin...

I agree. This mythical sword turns out to be a wrench/key. I'm fairly certain the key was not part of canon. Bad Reboot must be stopped.

Actually in a previous episode, one of the characters (I think it was Arondir) said it's most likely a key. So, we knew it fit into something but what exactly that is was unknown until now.

I thought it was a glorious scene, and a nice way to get rid of some of the characters that weren't really all that interesting. I mean, unless they somehow survive this, which they probably do in some kind of miraculous way.

And this show never claimed to be canon. It's a completely made up story based around middle earth and the LOTR/Hobbit lore/myths.

I hope Macguffin helped to "Take a Bite out of Crime"!

And why was a key even needed??? All that was needed was the tear down the dam ...

And there are so many questions: why was even a dam raised there? It's not like they have hidro electricity or something???

it was very late when i watched this last night , have I got this right

The weasley traitor guy puts the keysword into the , um keyhole.
This releases a huge amount of water stored in a dam at incredibly high altitude
That made a volcano erupt! and reign down fire & brimstone
Quite a lot of it in the little village but presumably all over the land.

... leading to your "why nuke the place you want to live in" comment.
How bad was it ?
are they all dead?
Is the ground fully scorched?

Hard to comprehend how much worse this show gets every. single. week. I'm actually down to watching it solely to see exactly how bad it can get.

So now we not only have Galadriel's turbo-boost horse (with some of the most hilariously bad special effects since the '70s), but apparently now she's completely immune to a pyroclastic flow and/or is trying to stop the eruption by making a mean face at the mountain. And of course, not bad enough totally making up ridiculous story elements, but basically making up physics and geology at the same time. Merely dumping even a lake's worth of water into a magma chamber (assuming that the tunnel to do that would even endure for long) is NOT going to make an apparently dormant volcano erupt that fast with that much force. And why is this even necessary at all (as others have observed)? This is more of what apparently passes for screen-writing these days where it appears the writers just sit around thinking "hey, wouldn't it be cool if this happened?" and then write it into the script with no back-story, motivation, reason or plot development. So instead of a plot, we have an endless series of disjointed, un-connected scenes that someone though it would be cool if that happened.