Is one allowed to get a Ephemeral Tattoo? https://startupbeat.com/ephemeral-temporary-tattoos/29634/ As you can see they’re exactly like regular tattoos with scratches in your skin but the ink is developed to be removed in 3 6 or 12 months so it’s not permanent.

Such a tattoo is definitely forbidden. The only question is, whether it is a Torah or a rabbinic prohibition. As I stated in the previous Responsa; The Shulchan Aruch (Yoreh Deah 180, 1-3) defines a tattoo as a scratch in his flesh that is refilled with ink or anything else that leaves a mark. Two actions are needed in order to transgress the Torah prohibition of tattoo, a scratch and writing within the scratch. These two actions; a scratch and writing within the scratch, exist in this tattoo. However, there are opinions among the Rishonim as to the length of time that the tattoo must exist, forever or for a long time. The question regarding this tattoo is, whether its prohibition is a Torah prohibition according to the Rishonim that it is enough if the ink lasts for a long time. Nevertheless, all of this is only regarding the Torah prohibition, but the rabbinic prohibition applies if one scratches in his flesh, even if it is not filled with ink. (See sources in the previous Responsa).