How concise can I get the Soulbond boilerplate in a homebrew card without functional changes?

Question

The Soulbond ability represents a couple of very long and wordy abilities:

When this creature enters the battlefield, if you control both this creature and another creature and both are unpaired, you may pair this creature with another unpaired creature you control for as long as both remain creatures on the battlefield under your control

Whenever another creature enters the battlefield under your control, if you control both that creature and this one and both are unpaired, you may pair that creature with this creature for as long as both remain creatures on the battlefield under your control.

Suppose I want to make a card with Soulbond, but I want to give it a way to pair with creatures other than these two ETB triggered abilities: specifically, I want to give it an activated ability that pairs it with something. I'd need to recreate Soulbond's rules text for the activated ability, but that's quite a lot of text to put on the card.

Sometimes, however, rules text is deliberately redundant just for clarity's sake — for example, Ashcloud Phoenix had a few words added to its first ability that only served to remind players of what the rules already did — so maybe not all of those words are strictly necessary, and just add clarity.

Under current rules infrastructure, if I'm homebrewing a card that has Soulbond and an activated ability that pairs it up, how much of the Soulbond boilerplate can I drop from that activated ability's text?

Or in other words, are these all functionally equivalent? At what point have I taken out enough that I've fundamentally changed the nature of Bonding? (Assume these are on a creature with Soulbond.)

• Full template:

  {T}: Choose a creature you control. If you control both the chosen creature and {this card} and both are unpaired, you may pair the chosen creature with {this card} for as long as both remain creatures on the battlefield under your control.

• Dropping most of the "if":

  {T}: If {this card} is unpaired, you may pair an unpaired creature you control with {this card} for as long as both remain creatures on the battlefield under your control.

• Dropping the "as long as":

  {T}: If {this card} is unpaired, you may pair an unpaired creature you control with {this card}.

Answer 1

All three templates are functionally identical.

The first and second are already very similar, although the first has the better wording, one that's typical for choosing something.

The third is very condensed, but the rules for "being paired" handle everything that happens to the pairing once it's been established:

702.94e A paired creature becomes unpaired if any of the following occur: another player gains control of it or the creature it’s paired with; it or the creature it’s paired with stops being a creature; or it or the creature it’s paired with leaves the battlefield.

The only purpose of the "soulbond" keyword ability is to establish the pair. Since your activated ability takes care of that part, even with the short third template, only the rules for "paired" are now of interest.

Overall I would recommend using the first template, simply because it explains everything there is to know about pairing right on the card, rather than requiring a look into the CompRules.

You could drop the words "on the battlefield" from the first template, because that's already implicit in "being a creature".

Answer 2

All three wordings have the same effect. The last one looks different in that it doesn't say that the bond goes away if control changes or they stop being creatures, but the rules cover that; the wording of soulbond is redundant.

With none of your wordings does the ability have a target. This has some minor effects, like allowing you to pair with a creature with shroud or protection and the not making you choose the creature to pair with until the ability resolves.

The first two could also be changed to say "this one" instead of "this creature", like the original.