This Seeking Tech guide will show you how to get the Cleared: Metal Slug X trophy from the PS4 version of Metal Slug Anthology.
This will unlock when you beat all six levels in Metal Slug X.
If you set the Continues setting to Free Play, then you will get unlimited retries to beat the game. You can also lower the difficulty if you want to.
You can find the video playthrough, along with the time stamps, below:
0:15 Mission #1
4:51 Mission #2
14:40 Mission #3
23:06 Mission #4
30:25 Mission #5
43:34 Final Mission