Planetary Destruction: When you reveal your force, you may place 3 "DRILL" special terrain markers on the map outside of starting areas. At the beginning of your turn, as a free action you may deal 1 penetrating damage to each character occupying a square containing one of these markers. At the end of your turn, as a free action you may place each of these markers into a square adjacent to its current square that doesn't contain another "DRILL" special terrain marker. When Imperiex is KO'd, remove these markers from the map.

Summon the Hollowers: Give Imperiex a double power action. You may place any of Imperiex's "DRILL" special terrain markers in different squares adjacent to Imperiex.

Entropy Unleashed: Imperiex can use Energy Explosion as if he has , Incapacitate as if he has , and Pulse Wave.

When exactly are the Drill markers placed on the map? The trait says to do so after you reveal your force, but you haven't even rolled for first player at that point, much less selected a map!
You are correct. The map hasn't yet been selected and this trait requires errata to correct the mistake. The exact change is still under review, but in all likelyhood it will be something like:

Planetary Destruction: After choosing starting areas When you reveal your force, you may place 3 "DRILL" special terrain markers on the map outside of starting areas. At the beginning of your turn, as a free action you may deal 1 penetrating damage to each character occupying a square containing one of these markers. At the end of your turn, as a free action you may place each of these markers into a square adjacent to its current square that doesn't contain another "DRILL" special terrain marker. When Imperiex is KO'd, remove these markers from the map.

Can the Drills move between different elevations?
No. To begin with, the Drills never move; they are placed. Heroclix makes a distinction between those two terms. Also, the Drills can only be placed into squares that are adjacent to their current location. Squares on different elevations are never adjacent.

This also means that you can't place a Drill in a square on the other side of a wall or in any other location that is not adjacent to its current location.

But what about ladders and stair?
Squares on opposite sides of a ladder or stair still aren't adjacent. The ladder or stairs creates an exception to normal movement rules, but as pointed out above, the Drills don't move. Adjacency is all that matters and there is no adjacency between squares of different elevation.

So if I put my Drill on an area of elevated terrain at the beginning of the game, it is stuck up there?
Yes and no. Yes, it can't normally be placed off the elevated terrain. However, Imperiex can use his Summon the Hollowers special power to replace the Drills adjacent to him. That could get the Drill down off the elevated terrain just fine.

Speaking of Summon the Hollowers, what is a double power action?
See the Double Power Actions entry for more information.

Can I put more than one Drill in a single square? And what happens if a character is sitting on top of multiple drills (either occupies a square with multiple Drills or has a larger base)?
To the first question: it depends. You may actually put more than one Drill in the same square when you first place them on the map. However, once the game begins and you start shuffling them around, you can not choose to place a Drill in a square that already contains another Drill. So stack them, if you wish, at the beginning of the game, but if you want them to stay that way you can't ever reposition them.

To answer the second question, the damage dealt to a character is not determined by the number of Drills. Instead, you simply check and see if it occupies a square with a Drill in the same square. If yes, then they are dealt 1 penetrating damage. If no, then they are not.