See Nyxian Overlay.

Creatures can't be attached to things by the rules, but cards trump the rules right?

Symbiotic is a creature type, like aura, that requires the creature be attached to something to survive. Symbiotic creature spells have a target.

Cards trump the comp rules, but can't always beats can

There's no instance of "can't" in 704.5p. 😛

These designs in particular aren't super serious, folks. I'm not too bothered about whether they work out or are good.

> cards trump the rules

And design considerations trump cards. Design considerations that caused the rules to be put in there in the first place.

If you want this kind of card, then it's not a matter of creating a new keyword, but a matter of arguing that attaching creatures to one another in the first place is a good idea.

This is exactly why soulbond doesn't use the "attach" concept, but creates a separate similar concept in "pair" in the first place: So the game correctly communicates that the two can "act and move" independently.

And from the reminder text you give you aren't committed to the creative theme enough to follow through on the "attached" flavor either, after all the vines can wander off on their own.

Soulbond and Bestow were created solely because the designers at Wizards wanted to avoid a rule that they themselves created. I don't see that rule as inviolable as they do. If players can understand Auras and Equipment, they should be able to understand a creature version.

As dude1818 mentioned, there are design/gameplay reasons for creatures not to attach: attached permanents are usually covered, in play, by what they're attached to; and a segment of the player base tends to tap attachments, which isn't generally indicative of their actual state. I would say it could also be confusing just how independent an attached creature would be of the creature to which it was attached. Counters on either creature might also get muddy.

I see the reasons dude pointed out as the primary ones for why they avoid attaching creatures to other creatures, but honestly, in a set with higher complexity allowance like Commander or Modern Horizons, I don't think it would be an issue for players. I think most of the issue is that the designers themselves have stuck themselves believing that they can't violate rules that they actually can.

Soulbond is, in my opinion, more complex than this. It should be harder to understand. Symbiotic creatures, as I present them, play almost exactly like Auras. Players already understand Auras and their functionality, so Symbiotic/Rely (or whatever they ended up being called) should take up very little thought space. Soulbond introduced a bunch of new terminology for little payoff. The creatures act a bit like Auras but they can't be stacked, you have to think about things entering the battlefield, and so many people I played with were confused about when they could pair their creatures. It was much less elegant of them to make up a new set of rules rather than just break the convention they've defined and make creatures that could just attach like Auras.

I could say similar things about Bestow.

> Soulbond and Bestow were created solely because the designers at Wizards wanted to avoid a rule that they themselves created. I don't see that rule as inviolable as they do. If players can understand Auras and Equipment, they should be able to understand a creature version.

It's not about "understanding". It's about playing things incorrectly even if you understand them. That's why tapping Auras did not ever make a return. Since the Future Sight test it has been confirmed that cards attached to other cards are harder to handle, because the stack mentally becomes a single unit.

Which is why soulbond despite actually in some regards being more complex than this (definitely not in the "attaching a creature to a creature that has a creature attached" department though ;) ) it plays better, because it moves players outside the mental box of attaching.

What exactly does "attaching" actually add to this keyword it wouldn't have if you just removed that second line from the reminder text and replaced the third clause with "This creature dies without that creature." or something like that?

p.s.: I think the pairing actually has more to do with the fact that it is symmetrical and it makes the mechanic much more useful to be double effective when two creatures with soulbond team up.

Also obviously there was a desire to avoid the 2-for-1 issue you are embracing here, so that's something that wouldn't get past R&D anyway.

If it wasn't clear before, I don't particularly care about these cards or this mechanic. I don't intend to actually implement it anywhere. At this point I'm just arguing for it for the sake of the discussion.