Hikari, Twilight Guardian [Modern Masters 2015] Junior Super Series The flashback cost is equal

The flashback cost is equal to that card's mana cost

then sacrifice it unless you pay its upkeep cost for each age counter on it

"The Rime of the Ancient Mariner"

Armageddon Clock deals damage equal to the number of doom counters on it to each player

Set: The Brothers' War Type: Enchantment Rarity: Rare Cost: {1}{R}{R} If a red or artifact source you control would deal damage to an opponent or a permanent an opponent controls

Hikari, Twilight Guardian [Modern Masters 2015] Junior Super Series The flashback cost is equalSet: Modern Masters 2015 Type: Legendary Creature Spirit Rarity: Uncommon Cost: {3}{W}{W} Flying Whenever you cast a Spirit or Arcane spell, you may exile Hikari, Twilight Guardian. If you do, return it to the battlefield under its owner's control at the beginning of the next end step.