Type 4, also known as Limited Infinity (LI) or DC10, is a casual, non-rotating, multiplayer format with two simple rules: everyone has infinite mana of all types but can only play one spell per turn. With Magic's extensive cardpool, Type 4 combines the bombastic spells and multiplayer element of EDH with the interaction of eternal formats. Pushing MTG to the extreme, Type 4 offers absurd boardstates, insane blowouts, and unforeseen interactions.

Rules
Players have infinite mana of every type at all times.
Players can only cast one spell per turn (spells cast for their alternate cost are also included in this).
Communal library for players. Players have their own graveyard.
Starting and max hand size of 7.
Starting life is 20.
All melded and transformed cards are played as is. Their MV is equal to the total melded cards MV or the front side of the card.

Serum Powder Mulligan or SPM - If a player is dissatisfied with their hand before the game begins, they may exile their hand and draw that many cards. Do this only once.
Alternate Cast Rule or ACR: Once per turn, you may cast an additional spell if it has an alternate cast that you pay.
Cards & Keywords that work under ACR (Currently in the stack. The list is not exhaustive):

Flashback (the card must be cast from the graveyard for its flashback cost to be considered alternate cast)

Foretell (the card must be cast from exile for its foretell cost to be considered alternate cast)

Madness (the card must be cast from exile for its madness cost to be considered alternate cast)

Morph/Disguise

Plot (the card must be cast from exile without paying its mana cost to be considered alternate cast)

BOOSTER TUTOR: if you play this spell you will get to open ANY SEALED BOOSTER from ANY PRODUCT and pick one card to add to the cube, we will both decided on how it works,and date and sign the card

Cards that state "You may pay rather than pay this spell's mana cost", e.g., Baleful Mastery, Force of Will, Ricochet Trap.
Cards that allow you to cast spells for free, e.g., Omniscience, Press the Enemy, Reinterpret, Spelljack, etc.
Cards that provide other cards with an alternate cast, e.g., Form of the Mulldrifter, Fist of Suns, and Jodah, Archmage Eternal.

For all other alternate cast cards, please refer to this page on alternate cast. The ACR is based on WoTC's definition and rulings on what constitutes an alternate cast.