Comments!
Cat:
Creamy:
The Great Underground Empire:
I voted for
Cat:
Spoiler
Quick and logical. I guess this one makes the most sense of all the solutions if the game is in the Monkey Island tradition of being able to carry anything. Something like this would probably be the first one would try, but the two part "smash brick -> use brick parts to make ladder" would make for a satisfying puzzle to solve nonetheless. I thought along the same lines, but decided to make the player have to drop most items before climbing.
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Creamy:
Spoiler
This one I would never have thought of!
I like the setup for minigames, and one could use the game setup to nudge the player along the way, for instance notating "Ladder part 1 of 5" in the inventory. Using the rat for a metal cutter had me laughing, but I doubt I would have seen that coming even if I was being nudged along every step of the way. If I managed to solve this, it would be extremely satisfying!

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The Great Underground Empire:
Spoiler
I thought of making a pile of the coal, too, but I thought it may be too shifty for practical use. I like using physics to make this an engineering puzzle, so to speak. This would be fairly logical and very satisfying to solve as a player.
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I voted for
Spoiler
Creamy's long approach. (Sorry, btw, for including the word "long" in my title, too. That was clumsy.) It may not be the most logical solution, but scores high in creativity/unexpectedness and regarding how satisfying it would be.
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