ESP8266-based boards, like
NodeMCU, Huzzah, WeMos D1, Seeed Wio Link, ... can run Blynk directly on the chip, using this board support package: https://github.com/esp8266/Arduino
Getting started with ESP8266: http://www.esp8266.com/wiki/doku.php?id=getting-started-with-the-esp8266
ESP8266 can't be powered directly from 3v3 pin on most Arduinos, as it requires more than 400 mA current supply.
ESP8266 flash might get broken. The code executes without problem right after flashing, but stops working after first reboot.
This WiFi module can somehow interfere with PIR sensors -> PIR sensor starts producing random values ;)
ESP8266 currently has troubles with connecting to WPA2-Enterprise networks, and WiFi hotspots that have Captive Portal (webpage that requires you to sign-in to get Internet access).
Low level debugging
In the IDE switch to Generic ESP8266 board.
In setup() add the following as the first line:
In the IDE set Debug port to
Serialand Debug level to
You will see a huge amount of debugging information in Serial Monitor.