How do I get the LIFT KEY in pokemon Leaf Green?

Answer 1

As soon as you enter the Rocket Base, head to the right and down, not the
stairs. Head to the left and fight the Rocket there holding two Level 21
Raticates. When you beat him, continue down to find an item ball containing
an Escape Rope. Now go down to Basement 2. Fight the Rocket as soon as you
see him holding 2 Level 17 Zubats, a Koffing, Grimer, and Raticate.

Now head down another floor to get to Basement 3. Fight the Rocket on the
lower path holding 2 Level 21 Machops and collect the TM21. Now head back and
to the right to the arrow maze. The maze looks mind boggling with so many
arrows, but it's not that difficult. There are arrows here representing the
direction you will be forced to go to until a different colored tile stops
you. From the side all the way to the right, take the down path to get a Rare
Candy. From there, your only option is to head back up so do so. This time,
start in the middle between the two arrows pointing away from each other. Go
left, walk down, and take the right arrow. You will have spun right past a
path. Go back and down that path and then walk left not taking any of those
arrows. Go down and there will be a second set of arrows. Take the one to the
top. As soon as you land there will be a Rocket waiting for you with a Level
20 Rattata, Raticate, and Drowzee. A pair of Dark Glasses will also be smack
in the middle of the path.

Head down the flight of stairs to Basement 4. Get the Ether on the table to
the left. Now go up, get TM49, and fight the Rocket member holding a Level 21
Koffing and Zubat. Beware, the Koffing can Selfdestruct for a lot of damage.
When you finish the battle, the Rocket will drop the LIFT KEY. Pick it up and
move head back to Basement Floor 2.

Answer 2

the lift key is in the team rocket hideout in the celedon city game corner. 1- fight the guy in front of the poster
2-push the switch on the poster
3-go inside the hideout and kick tail then get the lift key
4-good luck on your pokemon journey :)