I've recently been attempting to codify a set of rules for [one of the many variants of] Mental Magic. The elements I'm trying to include are:
Cycling, Ninjutsu, Flashback, Dredge, etc. shenanigans
For example, I want to be able to cycle a 2W card as Akroma's Blessing and then flash it back as Lingering Souls. This will have to involve designating what a card was (LKI). Most zone changes (other than stack-to-battlefield) need to re-'blank' cards, except for when they're being tracked: e.g., Undying and flicker effects shouldn't let you change the card's identity. Also, you can only name cards as you're "using" them (i.e. not just to make them henceforth-unnameable).
1 Utopia (basic land with no basic land types) per turn
Basic lands from outside the game can be found while searching libraries
...but they do still work, in conjunction with land-tutoring. Basic lands brought into the game can only ever be played as themselves.
Your Utopias are in quantum flux for purposes of their leaving play
Basically, Trade Routes and the like are still good, but do not let you cherry-pick from amongst the cards you've played as Utopias.
You can morph anything
If something gets turned face-up and its controller can't think of anything [new] for it to become, the opponent gets to choose; if they don't think of something, it just retains its [lack of] characteristics. (Also use this system when effects put permanents onto the battlefield.) Should come up rarely in practice.
Designation groups for less-common mana costs--NOT YET WRITTEN
For example, grouping all white/blue cards, or red X cards, or cards with BBB in their mana cost, or green cards with cmc >= 7.
What I've got so far:
Designation
By default, all cards in your hand, library, and graveyard are undesignated, with the exception of basic land cards (which are always simply designated as printed). Undesignated cards cannot be played, and their abilities do not function (though they still have them).
To designate an undesignated card, name a card with that mana cost that has not yet been named this way. You may do this at any time, as last known information if necessary, in order to
cast the card (from your hand, via flashback, etc.);
activate an ability of the card (Cycling, Scavenge, etc.);
have a triggered ability of the card trigger (Recover, Narcomoeba, etc.);
apply a replacement effect generated by a static ability of the card (Dredge, graveyard-allergic cards, etc.); or
turn an undesignated face-down card face-up via Morph.
Additionally, designate any face-up undesignated card that you put onto the battlefield or that you exile via an effect that will refer to that card, within the criteria of the effect moving it. For example, an effect that refers to Zombie cards in your graveyard or library will only see cards with "Zombie" printed (taking Oracle text into account) on them; and if said effect moves the card to the battlefield, it must be designated as a card that is a Zombie. As another example, if you exile a card in your hand to an effect that refers back to the exiled card (e.g. Isochron Scepter), you designate the card when you first exile it.
If you are required to designate a card, but you cannot think of anything, then your opponent may designate it. If they decline then it is designated as printed, even if this would repeat a name.
Designated cards retain their designation when moving from the stack to play. They also retain their designation when moving between zones if an effect is tracking them (Champion, flicker effects, Undying, Unearth, etc.).
Any other movement between zones causes non-Utopia cards to lose their designation.
Land
Searching for basic land
Any time you search a library, you may find basic Plains, Islands, Swamps, Mountains, and/or Forests from outside the game as though they were in that library (so land-tutoring effect work). A basic land brought in from outside the game can only ever be played as itself.
"Utopia"
Once during each of your turns, you may designate as a Utopia any undesignated card [that you could play as such] in order to play it, but only once per turn (so Exploration-esque effects do work, but only in conjunction with land brought in from outside the game). Utopia is a subtypeless basic land with the ability "T: Add one mana of any color to your mana pool."
Represent cards played as Utopias by placing them face-down (and, if necessary to distinguish them from morphed creatures, upside-down). (Note that this is merely for convenience; the game does not see them as being face-down, and any player can look at them.)
When an effect causes a player's Utopia to leave the battlefield, the physical card that leaves the battlefield is determined randomly from amongst the Utopias that that player both owns and controls. For example, Bob has three untapped Utopias in play: cards with printed mana costs W, U, and B. One of them has been enchanted by Fertile Ground. Bob taps one of the two unenchanted Utopias, and uses his Trade Routes's ability to return the tapped Utopia to his hand. He determines randomly whether to return the W, U, or B card, then rearranges the remaining two cards to accurately represent his remaining two Utopias.
Morph
You may cast any non-Utopia card as an undesignated 2/2 face-down creature by paying 3 rather than its mana cost.
Card-Specific
Judgment uncommon Incarnations (Valor, Wonder, Filth, Anger, and Brawn): You must control a land of the appropriate type in order to designate a card in your graveyard as one of these.
Dearly Departed: A Human must be entering play under your control in order for you to designate a card in your graveyard as Dearly Departed.
Banned
The following cards are banned (in addition to the cards banned in whatever format is being used):
This may be overly ambitious, but I would like to polish this to the very-shiny level of the current CompRules. It's been years since I guru'd, so any assistance with tightening up these rules would be appreciated (including stuff like grammar, style, arrangement ... and hopefully a less-clunky term than "designate")!
By default, all cards in your hand, library, and graveyard are undesignated, with the exception of basic land cards (which are always simply designated as printed). Undesignated cards cannot be played, and their abilities do not function (though they still have them).
To designate an undesignated card, name a card with that mana cost that has not yet been named this way. You may do this at any time, as last known information if necessary, in order to
Additionally, designate any face-up undesignated card that you put onto the battlefield or that you exile via an effect that will refer to that card, within the criteria of the effect moving it. For example, an effect that refers to Zombie cards in your graveyard or library will only see cards with "Zombie" printed (taking Oracle text into account) on them; and if said effect moves the card to the battlefield, it must be designated as a card that is a Zombie. As another example, if you exile a card in your hand to an effect that refers back to the exiled card (e.g. Isochron Scepter), you designate the card when you first exile it.
Designated cards retain their designation when moving from the stack to play. They also retain their designation when moving between zones if an effect is tracking them (Champion, flicker effects, Undying, Unearth, etc.).
Any other movement between zones causes non-Utopia cards to lose their designation.
Land
Searching for basic land
Any time you search a library, you may find basic Plains, Islands, Swamps, Mountains, and/or Forests from outside the game as though they were in that library (so land-tutoring effect work). A basic land brought in from outside the game can only ever be played as itself.
"Utopia"
Once during each of your turns, you may designate as a Utopia any undesignated card [that you could play as such] in order to play it, but only once per turn (so Exploration-esque effects do work, but only in conjunction with land brought in from outside the game). Utopia is a subtypeless basic land with the ability "T: Add one mana of any color to your mana pool."
Represent cards played as Utopias by placing them face-down (and, if necessary to distinguish them from morphed creatures, upside-down). (Note that this is merely for convenience; the game does not see them as being face-down, and any player can look at them.)
When an effect causes a player's Utopia to leave the battlefield, the physical card that leaves the battlefield is determined randomly from amongst the Utopias that that player both owns and controls.
For example, Bob has three untapped Utopias in play: cards with printed mana costs W, U, and B. One of them has been enchanted by Fertile Ground. Bob taps one of the two unenchanted Utopias, and uses his Trade Routes's ability to return the tapped Utopia to his hand. He determines randomly whether to return the W, U, or B card, then rearranges the remaining two cards to accurately represent his remaining two Utopias.
Morph
You may cast any non-Utopia card as an undesignated 2/2 face-down creature by paying 3 rather than its mana cost.
Card-Specific
Banned
The following cards are banned (in addition to the cards banned in whatever format is being used):
Please use card tags when you're asking a question about specific cards: [c]Serra Angel[/c] -> Serra Angel.