MARIO is a Super Mario World ROM hack pasta by SMW Central user Adam. The hack patch can be downloaded here. The patch itself is made by SMW Central user M A R I O, whose avatar is a SMW Mario without a face. He (she?) used to not to be seen as inactive (one month of no activity makes you inactive on SMW Central), as he (she?) posted mysterious and eerie things every now and then, just before he (she?) would turn inactive. As of recent, the SMW Central account has been disabled.
You can find the original thread here. *Note: You CAN download that link in the thread*
Appearance in Angry German Kid Series
The Angry German Kid Misadventures
It appeared in Episode 4: MARIO Leopold found it in the Attic and he played it and at the end BEN came out of the PC and starts fighting Leopold