"And here's the finished version of the level. I had three friends play this level, and observed how long it took them and what decisions they made. This is my chance to check difficulty level and overall quality of the puzzle. Ultimately, the player needs to feel like they solved the puzzle through some degree of skill, and not through trial and error."
Playtester A: "Not putting mouse on elevator at first, instead trying to send goat. Through platforming skills, could reach the second lightning machine, but that became the end of the line. Beat after about 5 minutes and 10 tries.
Playtester B: "Tries sending mouse along the wall to crawl past the reapers. Eventually makes it, but the lightning machines block the rest of that route. Switched to placing the mouse on the elevator, and got through in about 5 minutes and 10 tries.
Playtester C: "Figured it out on the second try!"
Verdict: "This one turned out great--a good combination of experimentation, logic, and skill in execution."