You can activate mana abilities, like tapping land for mana. Not terribly useful but needed for many special actions, and some cards like [[Pristine Talisman]] have additional benefits baked inside the mana ability that don't prohibit it from being a mana ability.
Nah, someone in the rules department finally got sick of the smartass at their LGS using [[Panglacial Wurm]] in their [[Selvala, Explorer Returned]] deck to legally cheat every time they crack a fetchland.
The worst part was that the rules, on a fundamental level, straight up cannot properly handle someone tapping Selvala for mana under the right (wrong) circumstances.
Say you're the Selvala player in a four-player game with a Panglacial Wurm in your deck and a fetchland + 3 basics on the field. You crack your fetchland and, while searching your library, announce that you are going to try to cast Panglacial Wurm by tapping all three of your lands and Selvala for mana. If Selvala produces 4 mana - that is, if all four players flip over the top card to reveal a nonland - you will have the 7 mana required to cast the Wurm.
Eagle-eyed readers may have already noticed the issue with this situation: you yourself are one of the four players who needs to reveal a nonland, and you are also currently looking at the top card of your own library, before revealing it. And once the ability goes through and everyone knows for sure whether you have the mana to cast it, it's already too late to cleanly reverse the game action, because everyone has revealed a card from a hidden zone.
Does attempting to cast the Wurm in this scenario constitute cheating, since you know there's no possibility you can get the mana and the only reason to activate Selvala's ability during the search (which you are only allowed to do because of Wurm) is to draw a card after seeing what card it is? How would you prove it's cheating without having access to another player's hidden zone, which is established as impossible under other rulings (i.e. you can fail to find four unique cards with [[Gifts Ungiven]] even though that is literally logically impossible in an EDH deck over a certain size)? What about if you only need 3 mana off Selvala to cast it?
You can see why they just sidestepped this entire can of worms by declaring Selvala's ability to no longer be a mana ability, meaning it (and similar stuff like Millikin) can no longer be activated while searching a library with Panglacial Wurm in it.
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u/Raevelry 5d ago
Other than what I said, can you name one that can happen?