Quote from ReapThaWhirlwind »This is over-the-top for a Leyline.
The interactive domain of the effect has too much impact, and would tip the scales at the start of the game (not fun). However, if you put this on a creature the same cost, then it would great (just as dynamic—and far more balanced).
Quote from user_938036 »That is a frighteningly complex card. You trigger on cast and then if the spell resolves a copy is created. Then you put a targeting restriction that is very easy to be impossible.
The worst part of the card is waiting till the original spell resolves to actually make the copy because that is a whole host of problems. The second biggest problem is the open-ended check for targets followed by the restriction on targets for the copy. The simplest example of a problem with that is a standard card Expansion/Explosion. If a player targets an opponent's creature to damage and themselves to draw the player with the creature can't actually copy the explosion because its targets are illegal, another obvious example is Switcheroo.
Quote from user_938036 »Looking at the card its intent is to make removal spells symmetrical meaning it wants to be played in a permanent heavy deck. However, it fails on multiple axis. First, this obviously does nothing if the opponent doesn't have the permanent types that are being targeted. If they have no creatures this card does nothing when they murder your creature. If they have no planeswalker they can Swift End without repercussion. With no enchantments, they can Nature's Claim without worry. So the card is trying to do something that just can't be done with the tools it has. Second because it only works on spot removal you are still wide open to mass removal.