Blood counter

Blood counters are a type of counter introduced in the Ravnica block that act as resources for activated abilities. They usually involve an exchange or sacrifice to be created after which they can be used as a resource on activated abilities.
==Description==
Blood counters first appeared on two artifacts in the Ravnica block. <c>Bloodletter Quill</c> from Ravnica: City of Guilds is the first card and artifact to use blood counters. Blood counters build up on the artifact per use of its ability and cause damage to the player unless removed via another activated ability. <c>Rakdos Riteknife</c> from Dissension also used blood counters as an equipment. Blood counters could be created on it by sacrificing creatures. The owner could then force a player to sacrifice a permanent per counter on the equipment if they sacrificed it. Ravnica Allegiance re-introduced Blood counters on the <c>Font of Agonies</c> enchantment which spawns blood counters whenever the player pays life allowing them to be later used to destroy creatures. 
Commander 2019 was the first non-Ravnica set to use Blood counters. Unlike the other uses, in this case a Legendary Vampire creature - <c>Rayami, First of the Fallen</c> - both exiles any creature that dies and places a blood cocunter on them. Rayami then gains up to 13 possible keyword abilities if any of the exiled creatures with a blood counter has those abilities.
==Trivia==
In Magic Online, the counter is colored green as its considered a positive effect and it shares an icon with Carrion, Corpse, Eyeball, Infection, and Plague counters.
==References==