Spellstone is still rolling as my current online card game. For some reason I always have one going. “Flavor of the month” is part of its design with “battleground effects.” Battleground effects last two months, and they give a boost to all cards from a particular race, faction, whatever. This is a not-horrible way to keep decks changing and to encourage people to spend money on new cards and upgrading cards. Unsurprisingly, the cash shop cards follow the flavor of the month, including introducing new high-end cards for that faction.
This month is an elemental defensive effect: elementals get a flaming aura based on their hit points, and anyone attacking them gets set on fire. “Scorch” burns out after two turns, except that if you get a new source of scorch it stacks and starts the two-turn counter over. All elementals have a scorch aura for two months, and a fair number of creatures have a scorch effect on their attack.
There is an event every weekend, usually an asynchronous PvP tournament. NPCs do not change their decks to follow the flavor of the month, but players do, and this is the first time to fight a large number of players who have switched over to elementals. PvP this month is just running around shouting, “my frogs are on fire and my dragon is on fire and the fire is on fire and everything is burning, aaaugh!”