So if I am understanding the situation right, I need to get to a floor above me to reach the minister, right?
If so, would it be ok to not go through the elevators at all? I know I cannot transfigure parts of things, but I figure Billy would know a "cut a hole in a wall" spell, and could cast it on the ceiling, then push himself upwards/transfigure himself into a bird and fly up, repeating until he's on the right floor to reach the minister.
If that doesn't work, how do you feel about people turning things into antimatter? Are there ready-made transfiguration spells that could turn, say, a dust mote weighing fractions of fractions of a milligram into antimatter? One milligram of antimatter would produce ~4.3 tons of TNT, so to have actual combat application it would need to be thousandths of that mass, which would get tricky, not to mention the world-changing applications of being able to transmute chirality at will [but that seems like something that would not be shared with muggles even under the loosest secrecy laws, for fear of antimatter warfare]
If I can neither blow them up with transfigured explosives nor just avoid them and go through the ceiling, I would like to bore through this corner and attack them from behind their barricade. It would probably lead to some casualties, but at least it is better than nothing. If that's not allowed, I think the easiest answer would be a barrage of Avada Kedavra, depending on if I could predict a reliable and safe exit vector for them, but that would require a detailed map and measuring spells at the very least, seeing as I would need to adjust for the depth of the ministry, the angle of the cast spell and the distance to the north sea, if it is even possible to avoid other underground populated areas, like deep basements or what have you.
the reason i didn't specify is i didn't want to stymie your creativity and you don't disappoint
cutting the ceiling and what scrimgeour did
so at the end of the post scrimgeour cut his way to the broom cupboard on his floor. He has escaped but is not out of the woods yet. Obviously you guys don't know that yet and just think he is being held and you need to get to him.
The basis for scrimgeour being able to do this is what dumbledore said to umbridge "that power still lies with the headmaster" my idea is there are some special powers that come with high wizarding positions like headmaster of hogwarts and in this case minister for magic. Scrimgeour can do this by virtue of that power but no one else can. If you cut the ceiling do this you will just hit brick, cut again more brick and so on.
antimatter
I'm going to go against this. I think we are going too far into the scientific... one weapons of this nature are very hypothetical and I dislike the idea of turning any form of matter into antimatter ie the distinct opposite of something. It is easier to transfigure something it if has similarities, as antimatter is the exact opposite of something I feel quite comfortable saying it is impossible.
killing curse
blackwell wouldn't let you anyway
I would like to bore through this corner and attack them from behind their barricade. It would probably lead to some casualties, but at least it is better than nothing
I'm happy with this....and it was the idea I had. When you bore through, you would have to break through 8 walls constituting four offices to get to the elevators. Will you take a small team through... a large team... will you take the barricade out from behind or will you sneak upstairs... whats your priorities?
if you want to cast any spells to check what's in the offices let me know and I will tell you the results. If you've got an idea outline your plan to Blackwell and I can get you moving :)
Let me know if anythhing is not clear, hope that's ok