I am getting a bit confused, sorry but I will try to summarize what I think is going on here.
I see your screenshot of the IDE monitor... however, if you have the USB-link running, you cannot also have the monitor! You must use the main USB
Serial on Mega for Blynk's connection to the server via the USB-Link. And you must delete or comment out
#define BLYNK_PRINT Serial and avoid any other
Serial.print() statements on that port.
On the Mega, if you want to use any extra hardware serial ports for monitoring, then use
Serial1, Serial2 or Serial3 (PINs 14-19), and utilising either a TTL-USB adapter or possibly Bluetooth, to another terminal program on your PC (I use termite).
In your shown example sketch, be sure to change all
Serial references for the email portion to one of the above optional hardware serial ports on the Mega.
I wouldn't try to mix the Bluetooth App link into the mix until you have gotten everything else working... besides the Blynk Bluetooth connection (and yes, currently only on Android) is really a point to point control link between App and hardware (instead of going through a server), not used as a serial data conduit.
I guess you could try to use BT it as the primary link to the App, if connecting the module to one of the extra serial ports, leaving the primary one for the IDE monitor, but I have not been able to get that to work on my end, either with TTL-USB or BT.