THREE QUESTIONS

[Legend]

THING 1
Thinking of using "+1/+1 vigilance", "vigilance lifelink" counters, etc. Is that possible without breaking something? Is it sensible or stupid?

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THING 2
I also want to Amass Shapeshifters, and ideally I want them to have changeling or to at least effectively have changeling (all creature types without the keyword), but I'd rather not have "changeling" in the reminder text. I'm looking for help with the wording. Can it even be done?

First is the current wording for Amass Zombies for reference, followed by the idea.

FOR REFERENCE
Amass Zombies 2. (Put two +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

THE IDEA
Amass Shapeshifters X, where X is the number of creature cards exiled this way. (Put X +1/+1 counters on an Army you control. It's a Shapeshifter with changeling. If you don't control one, create a 0/0 colorless Shapeshifter Army creature token with changeling first.)

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THING 3
Is it possible to splice onto an activated ability, like so?

Splice onto activated ability BB (As you activate an ability, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that ability.)

I don't want it to work with mana abilities. Does it need to say nonmana?

[Legend]

Idea 1 was indeed stupid.

I noticed that nesting keywords within reminder text is the norm now, so Idea 2 is fine.

That only leaves Idea 3. Does it need to say nonmana? Or is nonmana a given because mana abilities can't be targeted?

[WizardMN]

Nothing about Splice targets so not being able to target mana abilities doesn't really matter. If you don't want to splice onto mana abilities, which is probably the right way to do things, you will need to say it.

[Legend]

Nothing about Splice targets so not being able to target mana abilities doesn't really matter. If you don't want to splice onto mana abilities, which is probably the right way to do things, you will need to say it.

Would it be worded "Splice onto nonmana activated ability" or "Splice onto activated nonmana ability"?

[WizardMN]

Both read slightly weird in my opinion but either conveys what you need it to. Of the two, I probably prefer the first though I am not sure you are really wrong either way.

[spacemonaut]

You might want to just specify that Splice can't splice onto a mana ability, ever.

Splice onto activated ability [cost] (As you activate a non-mana ability, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that ability.)

Then in this alternate CR, we'd assume the Splice rules include something specifying you cannot splice onto mana abilities.

[Legend]

Oh yes, that's a much better wording.