It is an interesting idea to combine the Makeblock hardware with the Blynk app.
The MBot is basically an Arduino Uno, the firmware is open source and makes use of the open source Makeblock libraries.
The code can be found on https://github.com/Makeblock-official/Makeblock-Libraries/tree/master/makeblock/examples/Firmware_For_mBlock/mbot_firmware
The pin definition is shown on the MBot itself, and in the source you can find it in https://github.com/Makeblock-official/Makeblock-Libraries/blob/master/makeblock/src/MeMCore.h
It is possible to combine the Blynk libraries with Makeblock libraries. It should be possible to replace the Makeblock communication protocol with the Blynk communication protocol.
But, as far as I understand the question, the request is not to control the MBot totally using Blynk, but simply to switch it on/off. I don't understand the application of "turning on/off".
In case other people are interested in Makeblock+Blynk, give your ideas of how you see this (application), maybe I try to make it some day.
B.T.W. I would have liked to also control MBot using BLE, but unfortunately Blynk doesn't support the Makeblock BLE module. This is surprising, as it is basically a HM-10 module that can be used with every Arduino (without any other Makeblock component). The only difference is the ID, which is not identical to HM-10.