Mystic Forge

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

160 known combos.

• Sensei's Divining Top + Foundry Inspector + Mystic Forge
  Produces: Infinite card draw, Near-infinite storm count, Infinite draw triggers
  View on Commander Spellbook
• Sensei's Divining Top + Mystic Forge + Etherium Sculptor
  Produces: Infinite card draw, Near-infinite storm count, Infinite draw triggers
  View on Commander Spellbook
• Sensei's Divining Top + Mystic Forge + Cloud Key
  Produces: Infinite card draw, Near-infinite storm count, Infinite draw triggers
  View on Commander Spellbook

Combos: Commander Spellbook

Rulings

• 2019-07-12 · Wizards of the Coast
  Because you never "cast" a land card, Mystic Forge doesn't allow you to play an artifact land from the top of your library.
• 2019-07-12 · Wizards of the Coast
  Mystic Forge lets you look at the top card of your library whenever you want (with one restriction—see below), even if you don't have priority. This action doesn't use the stack. Knowing what that card is becomes part of the information you have access to, just like you can look at the cards in your hand.
• 2019-07-12 · Wizards of the Coast
  You still pay all costs for a spell you cast from your library, including additional costs. You may also pay alternative costs.
• 2019-07-12 · Wizards of the Coast
  You must follow the normal timing permissions and restrictions of the spells you cast from your library.
• 2019-07-12 · Wizards of the Coast
  If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast the top card of your library, you can't look at the next one until you're done paying for that spell.
• 2019-07-12 · Wizards of the Coast
  If the top card of your library has a morph ability, you can cast it face down from the top of your library, even if it's normally not a colorless card.

Rulings: Scryfall · Wizards of the Coast