I tried to look for that controller and barely managed to find it here: http://heromechatronics.com/en/core-details/
It appears that this controller is not yet available in the market as it has no details about it. Therefore it would be quite hard to do something with it.
But, since you wanted an Arduino MEGA compatible microcontroller but smaller I can suggest using:
The differences between them is that the Mega 2560 PRO MINI don’t have a USB connector and serial adapter (CH340) like the known Arduino pro mini, while the Mega 2560 PRO (Embed) do have them (so it’s more similar to Arduino mega).
The “Embed” board is a little bit bigger in size.
I think they should both be identified by the Arduino IDE as an “Arduino MEGA 2560”.
There’s a review about them here: https://idyl.io/robotdyn-mega-pro-mini-embed-arduino-review/
Ziv from circuito.io