1) Eraser goes down to the pit, then erase the land on the other side to make stairs to go up there.
2) Eraser goes and erase most of the spikes, but not all because there would be no spikes to pass, then he jump into the floorless pit but OVER the spikes, so he pass it.
3) Eraser erases the ground under him, then erases under the lava.