Alchemist

It's a good game :) and the music is pretty good, too :D

(Warning! Spoiler!"
To catch the mouse, walk to the spot with the chest and pull the lever. A rock will be released and rise toward the chest. However, you should wait until it reaches the top and then jump into the hole it leaves behind. You’ll reach a cave, climb onto the rock in front of the mouse’s burrow, and when the mouse comes out, you’ll jump on it.
To find the stone, climb to the spot where you collected mushrooms (the highest point of the tower, on the right, marked by the last rock). A text prompt will appear there, and then follow the transparent path to the right until you reach the stone.
Does anyone want the full walkthrough?

This game has pretty high system requirements, so it's possible that some people won't be able to run it, especially on computers running Vista :(

Great game, but you're totally right—FFTD, I agree, stebov

Can you give me some advice on how to get to a rock that I can't jump to and that there are no slabs leading to it?

I went through the whole thing in 540

How do I get a mouse?

Here are detailed instructions:
(SPOILER!!!) Follow the arrows to climb the tower (it’s on the map). The old man will give you a pouch of stardust. Go back and head to the spot where the dragonflies are flying and where there are moving stones at the edge. Pick up the orange-red flower and climb up to the outermost pillar above the moving stones. Then go right onto the invisible platform until you reach the rune stone. Jump down onto the sliding stones and hop your way across them until you see a lever. Pick that up, too. Then head back toward the little house. Two carnivorous plants are guarding another orange flower there. Pick it up (you’ll need to time it just right).
Below the little house is a sign with a purple mushroom. Go there. On the way, you’ll see a key—pick it up. Then continue on; you’ll come across a man who will cause orange-and-yellow mushrooms to appear in the field. Pick those up.
Then return to the man; he’ll give you a bottle of lamp oil. At the little house, pour the oil into the lamp and catch a firefly. Now let’s go catch a mouse. Go back to the spot where you were heading toward the tower. Jump down—there are lots of carnivorous plants and a few monsters there. Pick up the orange flower and keep going until you reach the chest. Open the chest and take the key from it. Then wait until the platform that took you to the chest is at the top, and jump into the hole beneath it. Climb up above the mouse hole and wait for the mouse to come out. Then jump down. Climb back up the tower, and about halfway up, near the lamp, climb down a little; you’ll see a man who’ll give you a root in exchange for the mouse.
Now all that’s left is to go back and throw it all into the cauldron.
(SPOILER)
Good luck! :)

How do I get to that rune stone? ;)

Correction: Where the flower was, at the highest point on the right; at the bottom right, you can see a tree.