My Brother Rabbit

This is story related and cannot be missed. It is unlocked when you finish the game. It may not be the final achievement. If you have not unlocked all 29 other achievements, "chapter select" will appear on the main menu and you can target the sections for the remaining achievements.

It is easy to unlock, but I'd like to add that this is a feel-good achievement if you have been following the overarching story of the game.

tldr for those who'd like a detailed explanation:
The final area is in the form of a clock with doors. To open the doors and trigger the finale, you have to attach various accoutrements. There are three Roman numerals on the clock--I, II, & III. Each corresponds to a screen with its own set of accoutrements.

I: Open space ship door, insert battery from stove burner. This opens space ship port giving you the cheese for triangle shape left of III on the clock. Take spade hanging on the stove & put it with the rake to the left of where you placed the cheese. The tire from the plane goes on the truck just above where you placed the cheese. Pinwheel from the basket goes with the other pinwheels to the right of the clock face. Take kite from plane & attach to kite string above the clock face.

II: Click on the balloons to the right to find a yo-yo. Attach it to the finger to the right of I on the clock face. Find a block in the baby carriage. Place it in the square hole to the right of I on the clock face just to the left of the yo-yo. There's a tower clock on the left hand side. To its right is a somewhat obscure puzzle piece. Connect it to another puzzle piece in a port to the upper right of the truck that got the tire in I. Remove the light bulb just above the now-connected puzzle pieces. Place it above the red light bulb to the left of the tower clock. This causes a train to emerge from the tunnel. Take the train & place it on the tracks to the right of the pinwheels.

III: Click on the saddle of the strange-looking duck horse on the right to find a somewhat concealed small red ball. Place it on the paddle to the left of the train you put on the tracks in II. Click on the tail of the strange-looking duck horse to find a carrot. Place the carrot in a small hat to the left of the slide on the left hand side of the screen. This causes a rabbit to appear in the hole next to it. Place the rabbit in the hat to the left of where you attached the kite in I. Below the strange-looking duck horse is a stool. Put the deflated soccer ball from the left hand side of the screen on the stool. You find it attaches to a small hose and is inflated. Place the inflated soccer ball on the foot just below where you inserted the spade to the left of the clock doors in I. The foot starts to kick the ball up & down. Above the strange-looking duck horse is a girl on the swing. Take her pirate hat and put it on the pirate just to the right of where you put the rabbit in the hat.

You need not place the items in any particular order. You can do each screen piece meal jumping around from one Roman numeral to the next. The sequence I used above was for ease of explanation and you can choose whatever sequence you like. Clicking around the screens at random will reveal most if not all of the objects. The placement of the objects is fairly intuitive.

When you place the last object on the clock contraption, the doors beneath the clock face will open. The rabbit 'playable' character will walk through these doors triggering a cut scene along with this achievement.