The mushroom ring is:
Code:
//Mushroom Ring
0001 0d0f 0000 0000 0002 0000 0d10 0000 0000 0001 0001 0d0e 0000 0000 0003 0001 0d11 0000 0000 0000 0002 0d0d 0000 0000 0002 0002 0d0c 0000 0000 0001 0003
Insert it into whichever item script you desire (I think kudos to Ry for figuring that one out). Mind you the problem with large multitile placements like this and the Yew tree are that if you are not using a fairly low density placement then you will have a lot of overlap.
As far as volcano, pretty much what Armada said. Except a few things I've found, for one, that tutorial is dated. People have shared some much better techniques for making mountains. Also the big thing is that the mountain surrounding for at least a few tiles out should be at the same Z level. I don't remember the current ranges, of course you can easily change it to suit yourself. Mod 10 right now (I haven't released it) I have 0,10,20,30,40 for lava. 5-100 for Mountain (increments of 5). I actually have a volcano on one of the test maps I was using (I like the one in Ilshenar) but no screenshots right now. It looks pretty decent. I made a crater in a mountain range at 40 Z and then I contracted the selection 3 pixels and filled it with lava 40.