There's a ruling on gatherer for Metallic Mimic that states the following:


For curiosity's sake I have been cruising the comp rules to see where the difference between a creature having it's ability defined by an external source vs being defined by itself causes this difference in the result for the +1/+1 counter replacement effect and I can't find it. Can someone point it out to me?
Thanks.

I believe the ruling is referring to stuff like Artificial Evolution or Blades of Velis Vel.

Edit: Although I did find this rule.



Which means Xenograft also doesn't work. Conspiracy alters the subtype on the stack, so I think it would work.

Conspiracy also doesn't work.

Ah, there we go, that's what I was looking for.

And yes, I also was interpreting the ruling in the gatherer page as referring to something like Xenograft when it talks about an external source.
This ruling is on the gatherer page for Xenograft:

Why wouldn't Conspiracy work? It causes the card to gain the creature type before it even resolves. Which means it should follow the direction of this bolded phrase right?:

Whatever ruling you give to Conspiracy should also apply to Artificial Evolution right? Since they both grant the subtype while the card is on the stack.

I don't see how Blades of Velis Vel fits into this picture?

The rule says "continuous effects generated by the resolution of spells or abilities that changed the permanent’s characteristics on the stack".

Conspiracy's effect is a continuous effect that changed the permanent's characteristics on the stack. But Conspiracy's effect wasn't generated by the resolution of a spell or ability. It's generated by a static ability. Static abilities don't resolve. So Conspiracy's effect is not taken into account.

Artificial Evolution's effect, however, was generated by the resolution of a spell, so it's taken into account.

I forgot AE could target spells.

Oh, ok. Cool.

Just for curiosity's sake would anything break catastrophically if the rules allowed replacement effects to check for changes due to continuous effects from external sources?

Catastrophically? Doubtful. Although I imagine it would make the explanation for what's happening more difficult to grok in most situations.

I wouldn't be opposed to such a change, though, as I feel that it would be more intuitive for Xenograft and Conspiracy to work with stuff like Metallic Mimic. But changing a rule just for the sake of two cards isn't exactly the most efficient way to do things.

How would it make it more difficult to grok?
Admittedly I'm only thinking of the situation with Xenograft and Conspiracy right now, but I'm having trouble coming up with a counterexample where the answer for the rules working the other way would be unintuitive.
I'm trying to come up with something and the first example I think of is that Painter's Servant could theoretically interact just like xenograft and conspiracy but I don't see any cards that have an etb replacement effect checking for color of the entering permanent so it's moot and also since it works the same way it would similarly be intuitive if I'm thinking about it correctly (which is always up for debate).

I admit that changing the rules to make only a handful of cards function differently is not ideal and I'm sure there was some particular reason why external sources were excluded, but I just can't put my finger on why.

Changing the rule would mean that Humility would creatures' stop replacement effects, so they wouldn't get their counters or their choices.

Humility always causes headaches.

While making Humility more powerful would not be ideal, would it really be unintuitive?

I don't think there've ever been any Humility interactions I would call "intuitive".

I think the current rule is good because it essentially says that we only have to take into account things that have already (irreversibly) modified the spell, what the spell itself says, and whatever changes we have already applied. That's very concise and chunkable. I don't know that a system which tells us to take into account, well, everything would be better.