If you were looking for the "Ancient" category of cards introduced in the Paradox Rift expansion, see Ancient (TCG).
Ancient Traits (Japanese: 古代能力) are special attributes given to certain Pokémon, starting in the Primal Clash expansion. They are not Abilities, and as such, effects that would prevent Abilities from activating (such as Garbodor's Garbotoxin or Wobbuffet's Bide Barricade) do not apply.
An example of a Pokémon card with an Ancient Trait
The Ancient Trait bar and text is placed at the top of the card, beneath the Pokémon's name. Apart from Pokémon-EX, Ancient Trait cards have artwork that differs from normal cards— the artwork extends down into the moves and fades into the bottom quarter, which is colored depending on the Pokémon's type. Because the artwork takes up most of the space available, the basic information of the Pokémon (Pokédex number, species, height and weight) is not shown.
Ancient Trait cards are treated as regular cards in play; they can be evolved from and into regular cards along its evolutionary line. A Pokémon's Ancient Trait does not depend on its type or rarity, though certain Ancient Traits are unique to the super-ancient Pokémon (Δ Wild and θ Max).
Whenever a Pokémon card with an Ancient Trait appears in a TCG set, a regular card of the same Pokémon appears as well (except for Pokémon-EX with Ancient Traits). Pokémon cards with Ancient Traits are usually stronger than their regular counterparts. Many of their attacks also take advantage of its Ancient Trait. Examples include α Growth Kingdra and Primal Kyogre-EX (which discard two Energy each turn) or α Recovery Eelektrik and Azumarill (which causes recoil damage and attacks more effectively with more HP).
α Recovery (Japanese: α回復α Recovery) is featured in the Primal Clash expansion. When a Pokémon with α Recovery recovers HP, the amount recovered is doubled.
Description: When this Pokémon is healed, double the amount healed.
α Growth (Japanese: αグロウα Grow) is featured in the Primal Clash expansion. When an Energy card is attached to a Pokémon with α Growth from the player's hand without using an attack, Ability or Trainer card, a second Energy card may be attached if the player has one in their hand.
Description: When you attach an Energy card from your hand to this Pokémon (except with an attack, Ability, or Trainer card), you may attach 2 Energy cards.
Ω Barrage (Japanese: Ω連打Ω Barrage) is featured in the Primal Clash expansion. A Pokémon with Ω Barrage may attack twice in a turn. If the first attack Knocks Out the opponent's Active Pokémon, the second attack hits the new one.
Description: This Pokémon may attack twice a turn. (If the first attack Knocks Out your opponent's Active Pokémon, you may attack again after your opponent chooses a new Active Pokémon.)
Ω Barrier (Japanese: ΩバリアΩ Barrier) is featured in the Primal Clash expansion and on Regirock, an XY Black Star Promo. The effects of the opponent's Trainer cards (other than Pokémon Tools and Stadium cards) do not apply to any Pokémon with Ω Barrier.
Description: Whenever your opponent plays a Trainer card (excluding Pokémon Tools and Stadium cards), prevent all effects of that card done to this Pokémon.
Δ Plus (Japanese: ΔプラスΔ Plus) is featured in the Roaring Skies expansion. When a Pokémon with Δ Plus Knocks Out an opposing Pokémon due to damage from its attacks, the player takes one extra Prize card.
Description: If your opponent's Pokémon is Knocked Out by damage from an attack of this Pokémon, take 1 more Prize card.
Δ Evolution (Japanese: Δ進化Δ Evolution) is featured in the Roaring Skies expansion and on two XY Black Star Promos. A Pokémon with Δ Evolution may be played to evolve a Pokémon during that player's first turn or the same turn it was put into play.
Description: You may play this card from your hand to evolve a Pokémon during your first turn or the turn you play that Pokémon.
Δ Wild (Japanese: ΔワイルドΔ Wild) is exclusively featured on M Rayquaza-EX, released in the Roaring Skies expansion. Due to this Ancient Trait, it takes 20 less damage from attacks from the opponent's , , , and Pokémon.
Description: Any damage done to this Pokémon by attacks from your opponent's , , , or Pokémon is reduced by 20 (after applying Weakness and Resistance).
θ Stop (Japanese: θストップθ Stop) is featured in the Ancient Origins expansion and on three XY Black Star Promos. Pokémon with θ Stop are unaffected by opposing Pokémon's Abilities.
Description: Prevent all effects of your opponent's Pokémon's Abilities done to this Pokémon.
θ Double (Japanese: θダブルθ Double) is featured in the Ancient Origins expansion. A Pokémon with θ Double may have up to 2 Pokémon Tool cards attached to it.
Description: This Pokémon can have 2 Pokémon Tool cards attached to it.
θ Max (Japanese: θマックスθ Max) is featured in the Ancient Origins expansion. When a Pokémon in play evolves into a Pokémon with θ Max, all damage is healed from it.
Description: When 1 of your Pokémon becomes this Pokémon, heal all damage from it.
, 
, 
, and 
Pokémon.
