Can a peanut base be elevated and grounded at the same time?

Assumption here is you are moving up stairs/ladder, etc. and don't have enough move to clear the lower elevation

No, a multi-base figure must end its movement so all squares are on the same elevation.

Squares of stairs/ladders are not adjacent for any purpose other then close combat attacks.

Yeah! I was right.

It's so rare I get a rule right. I gotta enter this in my journal.

Wow that is a big disadvantage for them then. You could sit one square away from the ladder/stairs on the elevated and they can't get to you at all (unless they have a movement power that helps). Interesting.

All I can picture in my head is a bully with a little kids hat dangling it above his head where he cannot reach.

"common, give it back!"

Yep. Rather annoying.