In every game, one should predict what to anticipate from the opponent based on their deck Purity, and take precautions as necessary, or at least know what to expect. I hope this list will be especially useful for new players. Test yourself: how many cards did you forget even existed?
Note that the list only includes cards which require prediction for a precaution. For instance, it does not include most, if not all characters with activated abilities as they must be in play before they get to activate their abilities, giving you at least 1 turn to react. Granted, one might want to plan 2 or more turns ahead, but then I have to list almost every card in Infinity Wars, which makes the list pointless.
The list does not include non-Core cards such as from the Star Trek set.
Cards are divided into factions, further divided into their required Purities, and sorted by cost. Cards with Dual Purity will be listed separately, and Hybrid cards will be listed twice in their respective factions, in 1 Purity subcategories. Common threats of significance, or threats too impactful to ignore even if they are rarely seen, are bolded.
Characters with Haste, Charge or Vigilance are grouped together within Purity subcategories if that's their only ability which requires precaution. Of course, if the character is the only one able to be grouped that way within the subcategory, there's no point in grouping. If the character has more abilities worth keeping in mind, such as Nix, it will not be included in these groups.FactionlessFlame DawnWarpathGenesis IndustriesDescendants of the DragonCult of VeroreExilesOverseers of SolaceSleepers of Avarrach
CoV+DoD: Jade Witch (if the opponent has at least 1 Verore card for Overcharge)
CoV+OoS: Angel's Bane (if the opponent has at least 1 Overseers card for Overcharge)
DoD+Ex: Tibat, the Mad Monk
DoD+FD: The Strength of Unity
DoD+GI: Enlightenator XT2500 (if the opponent has at least 1 Dragon Descendants card for Overcharge)
DoD+SoA: Infested Hero
Ex+FD: Lost Knight (if the opponent has at least 1 Flame Dawn card for Overcharge)
Ex+WP: Spawn, Fierce Companion, Once Was Clean (if the opponent has at least 1 Exiles card for Overcharge)
Ex+SoA: No More Heroes
FD+OoS: Ferocious Flyer
FD+SoA: Infested Knight
GI+WP: Dragon Collar