Plague counter

Plague counters are a type of counter introduced in Odyssey. They've behaved as both -1/-1 counters and as a type of upkeep tracking counter.
==Description==
Plague counters first appeared on <c>Traveling Plague</c> in Odyssey. It is an enchantment that when placed on a creature will create a plague counter on it with each upkeep. These counters will act as -1/-1 counters. They appeared once again on <c>Withering Hex</c> in Onslaught. The counters behaved the same way off of this enchantment but were instead created whenever a card was cycled.
<c>Plague Boiler</c> in Ravnica: City of Guilds saw their return as a resource. In this case, they acted differently in that they represented the regulation of the boiler. A plague counter was added to it at every upkeep and if more than three were on it then it would destroy all non-land permanents. It, however, had an ability that allowed a counter to either be added or removed as well as giving more control to the player for when it takes effect. 
==Trivia==
In Magic Online, the counter is colored green as it's considered a positive effect and it shares an icon with Blood, Carrion, Corpse, Eyeball, and Infection counters.
==References==