I think this is the crux of the problem. In its entirety Grapple gun reads:Problem 1: The space on the other side has to be "HIGHER" than the starting space. Why? The card says "up to 25 levels higher," which I think should included a height change of zero, maybe even negative (downward) changes in elevation.
"Instead of Sgt. Drake Alexander’s normal move, he may only move one space. This space may be up to 25 levels higher. When using the grapple gun all engagement rules still apply."
If the intent of the ability were that Drake could only land higher than his height, the ability should have been written:
". . .This space must be up to 25 levels higher. . ."
If one does what the card says, not what it doesn't say, it ought to play out like Drake has a height of 25 when moving up, but not down, for Grapple Gun. As such everything else is clear. Drake couldn't move through the overhang pictured earlier. He could move over ruins but would take falling damage for falling more than 5 spaces on the other side. He could fall to any height on the other side of an obstacle including a hight lower than his original.
I really hope the GG's aren't "updated" to play like Drake. I think the FAQ about only moving up is erroneous and should be changed.