You can outfit the Doom Slayer with a unicorn costume.
DOOM Eternal customization

If you dislike the dull green look that is common for the Doom Slayer in the latest DOOM titles, you're in luck. When DOOM Eternal releases, it will give players the option to personalize the look of their Doom Slayer in a variety of ways.

A new trailer for DOOM Eternal came out today that shows off some of the customization options. Unlike the older titles in the series, the customization options extend beyond simply changing their armor to colors like green, red, white, black, etc. In addition to the customizations that will be available for everyone, there is also already word about some exclusive Twitch Prime customization options. Those with Twitch Prime can link their accounts to their accounts in order to claim the "DOOMicorn Slayer Master Collection."

Conquer Hell’s armies in style! Unlock various skins, animations, and podiums by playing DOOM Eternal. Personalize your DOOM Slayer for photo mode and the single-player campaign. Then, slay with your friends in BATTLEMODE, where you can personalize your DOOM Slayer and playable demons.

For a limited time, get the exclusive DOOMicorn Slayer Master Collection included with Twitch Prime. Simply link your Twitch account to your account and claim this collection of skins, player animations, and upgradeable podium.
DOOM Eternal will be released on March 20, 2020 for the PlayStation 4, Xbox One, and PC. All pre-orders will get the Rip and Tear Pack that includes the DOOT Revenant Skin, Cultist Base Master Level, and the Throwback Shotgun Weapon Skin. Plus, Doom 64 will ship alongside the release of DOOM Eternal and is included with pre-orders. According to PC Gamer, Doom 64 will actually include a new episode with new levels not seen in the original N64 release, and will be capable of running at up to 1000fps.