The three-block puzzle goes through some neat iterations here, concluding with an enemy challenge. Sometime I should come back to this one and discuss it in specific. This is also the only stage in the game where you can block yourself from reaching the exit after grabbing the key.
5-2
You've got two important decisions here: how to push the blocks down on the bottom right there (by the arrow tile), and which arrow tile to flip first.
5-3
If you take the path with the arrow tile, you can't beat the stage. Why is the arrow tile there, just to trick the player? Also note that you have to kill a ton of snakeys in this stage, but that segment more or less plays itself.
5-4
5-4 solution
Take that, skulls!
5-5
In this one, you just have to watch the upcoming sequence of 3x3 tiles to make sure you don't walk into an arrow trap. There are even two cases, once on the bottom right and once on the bottom left, where you can put a block in an arrow trap so that you don't walk there. The blocks also create a challenge at the last minute when combined with that arrow tile and the medusa. Otherwise, I don't think the blocks add anything. In fact, you never need to use the blocks to cover the medusa's line of fire--everything is handled fine by the boulders.
The block/arrow tile setup at the top right can be solved using the three-block puzzle method, just excluding any moves you need to perform on the bottom block, since that's an arrow tile.
