Here is the full list of all 15 Bell Ringer achievements.
Win 500 multiplayer matches
Play Elvira for an hour
Win 250 multiplayer matches
Win 150 multiplayer matches
Play Alexander for an hour
Play Lucia for an hour
Play Gallows for an hour
Play Magnus for an hour
Win 100 multiplayer matches
Win 50 multiplayer matches
Win 10 multiplayer matches
Win a multiplayer match