The X series is a series of portable game systems that contain built in games. You can install your own games as well. They are made by a Chinese company (possibly Powkiddy or Coolbaby) They are similar to MP5 game consoles.
List of game consoles
X2 - The first known console in the X series. It resembles a Game Boy and plays NES/GB/GBC/GBA/MD games.
X5 - Resembles a PS Vita and plays the same games as the X2. It is more common in Asia,
X7 Plus - Colors look like a Nintendo Switch and resembles a PS Vita. Plays the same games but has fuzzy image glitches.
X12 - Looks exactly like the X7 Plus but has different hardware. It doesn't play games well and crashes them.
X15 - It runs Android hardware. Also allows gameplay of PS1, PSP, Dreamcast, N64 and Nintendo DS
X16 - This is distributed only by Powkiddy and has different games. It has better emulation and also plays Neo Geo/MAME games. It also resembles a PS Vita
X18 - It resembles a Nintendo DS and is similar to a GPD XD and also runs almost the same hardware.