From Takubon 18: Sailormoon, Sailorchibichibi and Princess Kakyuu gets surrounded by a mist and we see a butterfly appear. When it clears a little, they discover a huge display of graves in front of them. SailorHeavyMetalPapillon appear with maybe thousands of butterfiles surrounding her, she tells them that this is the last place the dead stars come to, and that the butterflies were the dead planets and stars. From benid her (yes if you look closely), we see a little funeral procession where these people dressed in black hoods carry a coffin across the cementry. Princess Kakyuu discovers the Sailor Starlights' graves 0_o and Sailormoon points at two figures not that far away who were digging a grave, there was a coffin beside one of the grave diggers. "It looks like someone is going to be buried here soon......" HeavymetalPapillon said, when Sailormoon and Co. looked closer, they discover that it is their own graves. Huge vines shoot out from the ground and grab the three of them from behind. "What a pity, the next grave will be yours!" HMP shouts, Sailormoon says "No!" :) HMP goes on to introduce herself as "the last of the Sailor Anima Mates and the hunter of souls Sailor HeavyMetalPapillon!" she guaranteed that their funeral procession would be a lovely one (haha...). To let them die a painful death, HTMP chose to destroy them with Fire. Flames leap up and start burning Sailormoon and Co.when there's a flash in the sky, SailorChibiChibi looks up and sees Chibimoon and Co. (the Amazoness Senshi) who blasted the vines, attacked HMP, and killed her :(
HMP is most probably a citizen of Planet Butterfly who was ordered by Galaxia to assasinate the sailor senshi from that Planet. if she did it, she could take the senshi's place, this was how LeadCrow and TinNyanko became Anima Mates otherwise HMP could have been good until Galaxia took away her starseed and gave her the wristbands so HMP turned evil and work for Galaxia, it worked this way for the senshi in both the anime and manga.Papillon, most of you should know by now, is French for Butterfly. Which explains those cool butterfly wings she has and all those butterflies that she has.