Wall of Roots

[PalladiaMors]

On the "list of unsupported card groups" topic, I was listing these as unsupported:

Activated abilities that generate mana (Deathrite Shaman, Wall of Roots, Squandered Resources, Agent of Stromgald).

This has just been disproved, since Wall of Roots was added. I admit I was actually pretty unsure of what I was saying in this particular case.

What's the proper wording for this group of cards? I see now that the problem isn't related to being a mana ability or an activated ability. I think I remember melvin once said that the problem is that mana producing cards shouldn't have choices. Wall of Roots doesn't require any choices, while Shaman requires a target choice, Squandered requires choosing a land to sacrifice, and Agent the mana source to pay for the ability. Is that the key difference? I'd appreciate if someone could suggest a wording for this group.

Edit: Oh yeah, if anyone has spotted any other errors in that list, please do tell me. I'd rather not provide wrong information to people.

[melvin]

May be easier to state what is supported, which are activated mana abilities that can be activated at most once to pay for a single mana cost without any choices.

Deathrite Shaman's ability is not a mana ability as it has a target.

Squandered Resources's ability requires a choice and is repeatable (violates the at most once restriction).

Agent of Stromgald's ability requires a choice and is repeatable (violates the at most once restriction).

Putting a counter as in Wall of Roots is also repeatable, but the "at most once" requirement is restored by the activation condition "Activate this ability only once each turn"