Echo of Eons

Bracket

• B1 Exhibition — allowed: No restriction at this bracket
• B2 Core — allowed: No restriction at this bracket
• B3 Upgraded — allowed: No restriction at this bracket
• B4 Optimized — allowed: No restriction beyond the banned list
• B5 cEDH — allowed: No restriction beyond the banned list

Why

• No Game Changer, mass land denial, extra turn, tutor or two-card combo

How Lotus Vault estimates a bracket

Bracket: Lotus Vault analysis, with Commander Spellbook flags

Combos

22 known combos.

• Nekusar, the Mindrazer + Echo of Eons + Phyresis
  Produces: Each opponent loses the game
  View on Commander Spellbook
• Razorkin Needlehead + Echo of Eons + Phyresis
  Produces: Each opponent loses the game
  View on Commander Spellbook
• Fate Unraveler + Echo of Eons + Phyresis
  Produces: Each opponent loses the game
  View on Commander Spellbook

Combos: Commander Spellbook

Rulings

• 2021-03-19 · Wizards of the Coast
  To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.
• 2021-03-19 · Wizards of the Coast
  A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.
• 2021-03-19 · Wizards of the Coast
  "Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."
• 2021-03-19 · Wizards of the Coast
  If a card with flashback is put into your graveyard during your turn, you can cast it if it's legal to do so before any other player can take any actions.
• 2021-03-19 · Wizards of the Coast
  You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.
• 2021-03-19 · Wizards of the Coast
  You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.
• 2019-06-14 · Wizards of the Coast
  Echo of Eons won't be put into your graveyard until after it's finished resolving, which means it won't be shuffled into your library as part of its own effect.

Rulings: Scryfall · Wizards of the Coast