Oooh, neat mockup!

See Image tab.

"Cards with dark mana in their cost (or alternate cost) are violet toward the bottom."

See Mystic Mycoplasm.

Testing some overlay options and iterating over a design by Link.

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See Urborg's Unrest.

Precedence for a flexible wording in custom sets. Amass defaults on two parameters:

1. "Ooze" is the parameter describing what gets the +1/+1 counters. It defaults to "Army".
2. "green" is the parameters describing what additional characteristics the token gets if it is created. It defaults to "black Zombie".

See Llanowar Contingent.

Precedence for a flexible wording in custom sets. Amass defaults on two parameters:

1. "Army"/"Swarm" is the parameter describing what gets the +1/+1 counters. It defaults to "Army".
2. "black Zombie"/"black Spirit with flying" is the parameters describing what additional characteristics the token gets if it is created. It defaults to "black Zombie".

Precedence for a flexible wording in custom sets. Amass defaults on two parameters:

1. Army is the parameter describing what gets the +1/+1 counters.
2. green Elf is the parameters describing what additional characteristics the token gets if it is created.

Planeswalkers with static abilities.

­Teferi, Temporal Archmage is one already, but let's try for something that's most relevant on the battlefield.

Planeswalkers with static abilities.

­Teferi, Temporal Archmage is one already, but let's try for something that's most relevant on the battlefield.

@dude1818: Loyalty abilities are activated abilities, so you can't put the static ability inside it like you do for the +1. It might be possible to word it like Deadly Designs, but for walkers. "+1: yada yada. You may activate this ability for any planeswalker you control." It would need to be written out in the comp rules, but that sensibly translates to "you can activate this ability using a different walkers one use per turn and the loyalty cost applies to that other one, but Liliana is the one causing the life loss." That last detail matters for targeted effects and protection.

So if I have to write new entries into the comp. rules, why couldn't I write them for the phrasing I use as well? I actually considered your wording, but rejected it because no matter the entry in the comp. rules, players would not unambiguously be able to tell the source of the ability and which planeswalker uses up their use of a loyalty ability. And really if I wanted the functionality you suggest (which only applies to the cost and no other aspect of the ability), then I have two easier alternatives from the top of my head:

"You may pay this ability's cost with any planeswalker." (Would remove any ambiguity about whether the ability affects anything but paying the cost) or

"[0]: Each opponent loses 2 life. Put a loyalty counter on a planeswalker you control." (For a minus ability I could even use "If you do" wording)

So I wouldn't even go for a special wording, but just do the second one. My goal though is to allow the ability to be activated multiple times - once for each planeswalker.

@jmgariepy: Alternate wording would be a sentence before the activated abilities. Something along the lines of "As long as Liliana of the Gatewatch is on the battlefield, all planeswalkers you control have all of her activated abilities."

Possible, but requires the use of a four ability frame and is functionally different - especially the second ability changes its Math considerably if it can be passed around like that, so I want to be more selective.

What would be wrong about a comprehensive rules entry like this:

Some activated abilities read "[Ability] Each [permanent] you control also has this ability." That phrase represents an additional static ability and means "Each other [permanent] has '[ability]'." The permanent itself has the activated ability as well.

?

BTW: If this solution wouldn't work it's entirely possible to type out "Each planeswalker you control has '[+1]: Each opponent loses 2 life.'" This wording tries to preserves aesthetics and text box real estate.