You need:
- Charles 3.4.1
- Firefox

Step to step instructions:

1) Open Charles
2) Enter Sky City (click the logo above to play directly on facebook)
3) When game is loaded, Expand “http://games.mmo2.myfarmvillage.com”
4) Expand “skycity_en\ajax\”
5) Right click the folder “ajax” and select Breakpoints
6) Refresh Sky City. The game should hang and a breakpoint tab appears on Charles
7) Click Execute 4 times. You should now be able to edit the response of “user.php“
Click ‘Edit Response‘
9) Click ‘Raw‘
10) Change the credit value to 88888.
11) Click back on the Structure tab and right click the ‘ajax‘ and select Breakpoints again
12) Click back on the Breakpoint tab and click Execute until all the breakpoints are gone.
13) The game will now load and you should have 88888 credits. Spend them now as it will be gone when you refresh.

This credit cheat can be used for 2 other games: My City Life and Farm Country and the steps are similar.
You can also watch the video-tutorial below:
Credits to : pwnthis.net

You need:

Charles 3.4.1
Firefox
Flash 10

Step to Step guide:

1) Open Charles
2) Play My City Life
3) In Charles, find for the url ‘games.mmo2.myfarmvillage.com’
4) Expand > Expand ‘City Life’ > Expand Definitions
5) You should see ‘Buildings…’, ‘Decorations….’, ‘Terrain…’
6) Right click Decorations and select Breakpoints
7) Refresh My City Life. The game will freeze at the loading and a Breakpoint tab will appear on Charles
Click Execute
9) ‘Edit response’ tab now appears. Click that.
10) Click HTML
11) First item on the list is ‘Road’. Change the value of ‘Sell’ and ‘plantXP’ to 999999
12) Click back on the Structure tab, and right click Decorations and select Breakpoints
13) Click back on the Breakpoints tab and select Execute
14) Now the game will continue loading… Buy a road and watch your exp rise. Sell it and you will gain the amount of coins you input in step 11.
15) ¡Enjoy!