Alright.
1. Download this little Script:

2.Open cheat engine (Don't open the Script yet)
3.Select LolClient.exe
4.Value Type: Array of Bytes
5.Untick Writable below..
6. Search for 89 4A 14 8B 4D F0 89 0D
7.Couple of adresses will be shown.. Select the 4th adress from the bottom
8.Copy the adress (For example 16B1FCA2, Adress is always different after relogging..)
9.Now doubleclick the Script you downloaded above, it should open Cheat Engine with 2 Adresses at the bottom.(LOL Script - by Spudgy and Mastery Point)
10. Doubleclick <script> at LOL Script - by Spudgy
11. A new window should open
12. Replace dd 0 with dd 7
13. Replace BAADF00D with the adress you copied before ( 4th adress from bottom, remember??)
Note: There are 2 BAADF00D's.. you have to replace them with the adress you got earlier.
14. Now choose LolClient.exe on the Scripts Cheat Engine Window and Tick LOL Script - by Spudgy and add one point to Mastermind
Make sure you do not have negative mastery points on the left side.. else you wont be able to save