The questions with this card are:
1. How could this see print?
2. Does it work within the rules?
-Instant Land-
Legendary Land
You may play ~this~ any time you could play an instant.
T: Add 1 to your mana pool.
-Flavor text-
It has to be a Legendary Land as a very basic drawback. I also see this as being in the uncommon slot, so that in draft it's Legendary status will be applicable. Also, I'd hate this to be a chase rare. But that isn't enough to offset an otherwise unpunished 3 lands on turn 2.
Possibilities include:
T, Pay 2 life (more/less?): Add 1 to your mana pool. (Life loss isn't an issue in decks where this would be broken.)
T, Sacrifice ~this~: Add 1 to your mana pool. (Is a bad Lotus Petal still good?)
T, Sacrifice a land: Add 1 to your mana pool.
3: ~This~ becomes a copy of target land and gains this ability. (Was saving this for a separate land, but it does work here too. Doesn't necessarily need to have "and gains this ability.")
When you play another land, sacrifice ~this~. ("Borrowed" from City of Traitors. It's similar to the Lotus Petal version when you break it down.)
When another land comes into play, sacrifice ~this~. (More emphasis on timing.)
So, rules.
305.4. During either main phase, the active player may play one land card from his or her hand if the stack is empty, if the player has priority, and if he or she hasn't yet taken this special action this turn. (See rule 212.6, "Lands.") This action doesn't use the stack and it isn't a spell or ability of any kind. It can't be countered, and players can't respond to it with instants or activated abilities.
408.2d Playing a land is a special action consisting of putting that land into play. (See rule 212.6, "Lands.") A player can play a land only during a main phase of his or her turn, when he or she has priority and the stack is empty. The player who played the land gets priority after this special action.
212.6a A player may play a land card from his or her hand only during a main phase of his or her turn, and only when he or she has priority and the stack is empty. A land card isn't a spell card, and at no time is it a spell. When a player plays a land card, it's simply put into play. The land card doesn't go on the stack, so players can't respond to it with instants or activated abilities.
Should "You may play ~this~ any time you could play an instant." really be "You may play ~this~ as a land during any player's main phase."? That still feels like it leaves too much rules baggage. I think what this needs is an alternate route of putting it into play, i.e. "Something, and
put ~this~ into play." but that steps around the whole premise of the card, which was breaking rules. It does mean that players don't need to concern themselves with the vagaries of the rules that I wasn't really even aware of until I started looking into this.
So, I think the answer to the rules problems is a simple "put ~this~ into play" effect with "Play this ability only during an opponent's turn." (templating that hasn't been used since Tempest and has mainly been used for Siren's Call/Festival effects.) Unless someone convinces me otherwise. I'd be ecstatic if they did.
How can this be playable without being terrible? Don't forget to take all relevant formats into consideration!
Current Wording:
-Instant Land-
Land
~This~ comes into play tapped.
: Put ~this~ from your hand into play.
: Add 
to your mana pool.
-Flavor text-
Changes:
- removed Legendary
- changed main functionality
- added CIPT
