The Sims Team left some bits and pieces of the upcoming The Sims 4 Vampires Game Pack in the latest game update. One of the things they left are the visuals of a ghost who died from sunlight. This type of death can normally be caused by a vampire who gets exposed to sunlight for too long.
To trigger this death and turn your Sim into a ghost who died by sunlight instantly, simply enter the testingcheats true + traits.equip_trait Vampire_Sun cheats.
Tip: @Nuclearxpotato
