Rarity
From Archon Arcana - The KeyForge Wiki
A card’s rarity symbol can be found at the bottom of the card, near the collector number. A card’s rarity (common, uncommon, rare, or special)is used by the deck-generation algorithm to determine how frequently it will appear in decks. Special cards have a different type of distribution and do not obey the game’s standard rarity rules.
—KeyForge Master Rulebook v17.4 September 2024
There are three types of special rarity that the deck building algorithm uses, according to the Master Vault: