In the DC Universe, Bgztlian are human-like beings inhabiting a world that occupies the same location as Earth, but at a another vibrational plane. All Bgtzlians possess the ability to become incorporeal. Here's a "Phantom Folk" race for 5e based on them:
Bgtzlian Racial Traits
Ability Score Increase. A Bgtzlian can improve one ability score of their choice by 2 points and another by one point.
Age. Same as humans.
Alignment. Any.
Size. Bgztlians are Medium.
Speed. Base walking speed is 30 feet.
Languages. Bgtzlians can speak, read, and write Bgtzlian and Common.
Phasing. As a bonus action, a Bgtzlian can become incorporeal, either entirely or only a part of their body. While incorporeal their movement becomes flight, and they move through other creatures and objects as if they were difficult terrain. They takes 5 (1d10) force damage if it ends its turn in side an object. They are immune to nonmagical damage while entirely incorporeal. Anything nonliving they are carrying or wearing becomes incorporeal as well, but they are unable to manipulate any new objects, or make attacks or cast any new spells.