Split card to the next logical iteration. Play either half from hand xor graveyard. When a spell is put in the graveyard from the stack, turn the card 90 degrees so that the other half is exposed to signify that that half can be cast from the graveyard. However, put the card normally in the grave if both halves of the same card have been cast this game or if it was put there by other means.

The restriction to cast from the graveyard is per instance of the card. Each card in your deck is counted separately. The restriction is forgotten if the card is moved to another zone besides the stack.

Ex. You cast Bears from the hand. You put the card sideways in the grave so that Guns is exposed to signify that you can cast Guns from the grave. You draw another copy and cast Guns from the hand. This time expose Bears in the grave. So now you have one card showing Guns and another showing Bears in the grave.

Adjoining word is "with". e.g. Bears with Guns

This has memory issues (how would a random dude know how to tilt this card?) and is just waaaayyy too confusing as it is IMO.

I would specify in the reminder text if "haven't cast that half this game" means as in from anywhere or just from graveyard. I don't think cards as game objects really know if they have been cast or not this game once they move from a zone to another (such as hand to grave). If it would retain that knowledge, it would have weird implications. What if it's returned to hand? What if it's put on top of library? What if it's shuffled into a library?

This doesn't work. The game requires every copy of a card in a deck to be identical, so you can't track that this particular still has Bears available, but this one has Guns. You would have to refer to it by name, which makes it terrible to run multiple copies in a deck.

I say it works, so it works. people write the rules; they dont write themselves.

It breaks everything else though. Most rules exist for a reason, and this is definitely one of them. If an object changes zones, there must not be a way to identify it, because you physically can't if it goes to a hidden zone or one that's unordered.

dude have you checked out the Amonkhet spoilers? they literally designed the frames so it sticks out from other cards in the grave. so you can tell if a split card can be cast from the graveyard. my idea is the same, the only difference is either half can be cast from graveyard.

also Skullbriar, the Walking Grave which says "Counters remain on Skullbriar as it moves to any zone other than a player's hand or library." so yea they already found an exception to identify cards that move between zones.

The problem is that your reminder text doesn't explain the ability well enough and dude1818 justifiably expects this ability to be intended to track information in a way that has severe logistical issue or memory issues.

The problem has already been pointed out by Tahazzar: The reminder text needs to be more specific.

Since a player doesn't get to read the magicmultiverse-comments, the reminder text has to do that job - and so far the reminder text does that job poorly.

A great way to help with that issue is exiling the card during one of the two stages.

So its reading comprehension issue. Sagas have terrible reminder text.