A couple enchantments

[Unrelated]

Memory Leak

1BB

Enchantment

Whenever any player plays an instant, that player loses X life where X is equal to that spells converted mana cost.

Focus - Instant (Whenever a player plays an instant, any player may pay XX, if they do, Memory Leak's controller loses X life where X is equal to that spells converted mana cost. Memory Leak's controller draws a card.)

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Demanding Aura

1BB

Enchantment

Whenever any player plays a sorcery, that player loses X life where X is equal to that spells converted mana cost.

Focus - Sorcery (Whenever a player plays a sorcery, any player may pay XX, if they do, Demanding Aura's controller loses X life where X is equal to that spells converted mana cost. Demanding Aura's controller draws a card.)

[marhawkman]

Um... counterspell isn't a card type...

[hachihyaku]

Focus is templated wrong.
It should be:

Focus - <type> (All <type> cards have "As an additional cost to playing this spell, you may play <X><X>, where X is the converted mana cost of this spell. If you do, <this>'s controller loses X life and draws a card.")

Only the player of a spell can pay additional costs, and X needs to be defined or else they can pay whatever they want for it.

Nobody is ever going to Focus anything, BTW. It costs way too much. (Why would you play a 3 cmc spell and then pay an additional 6 just to make your opponent lose 3 life AND draw a card?)

[Unrelated]

It's set up so that Anyone CAN play the Focus. And (X) is defined as the converted mana cost of the spell that is being played. For instance:

Player 1 has Memory Leak on the Table.

P1 attempts to play Llanowar Elf.

Player 2 plays Remand.

P1 pays 4 for the focus effect.

P1 loses 2 Life and draws a card. - Via Focus Effect

P2 loses 2 life. - Via Memory Leak

P1 puts Llanowar Elf back into his hand. - Via Remand

P2 draws a card. - Via Remand

I'm sure there are better examples out there.

[hachihyaku]

Then it's not an additional cost.

As you're describing it, it's:

Focus - <type> (Whenever a player plays a ~type~ spell, any player may pay <XX>, where X is the CMC of that spell. If a player does, that spell's controller loses X life and draws a card.)

I'm assuming the ability can only be played once; if it can be played several times, it's broken.

[Unrelated]

Updated wording on the cards.