Are you using a DS or an emulator?
If you are using a DS, there could be a glitch or problem with you DS or cartridge, or the game is hacked.
If you are using an emulator, there may be a problem with your game file, or something is wrong with the cheats that you are using.
Some possible reasons :
- Your Greninja or that Regirock may be hacked.
- Your eyes could be playing tricks with you.
Also, You should provide more details of your game. I try to edit the answer.
Edit : As you said, you were playing an unofficial game/website. Well of course there will be errors or glitches since it is not official. If you still have problems, you should find the developer yourself and not ask questions about it on this site since this is not allowed.