Grim Reaper is a Damashigami. They are numerous, and tend to wear costumes to deceive unwitting victims.
It's a simple skeleton wearing a black hood.
One appeared in Rinne’s room in the abandoned club building, disguised as a Bear Doctor, claiming he and his wind-up assistant came to treat Rinne from a cold, but their motifs are discovered and Rinne vanquishes them both.
Many would try to trick Sakura into giving them money, disguised as restless spirits, and also support her and Rinne to get married to support Sabato’s second attempt to make Rinne inherit the Damashigami Company, only to fail.
When Ageha ran after Sabato and her sister, many used different deceitful tactics while wearing many costumes, to earn money from Ageha, only for Rinne to expose them, and to convince Sakura to accept the wedding ring only for her and Rokumon to unzip them.