Not many mana abilities can be activated from exile.

The intent is that you could add mana if you exile a land. Can that be made to work? I posted a question regarding this to MTG Salvation.

Yeah, but this SAYS that you can activate it. I think that trumps. Anyway, wording aside - seems legit. Always at least mill-1, a third of the time it's a mana rock of a random colour; and just occasionally it does something bonkers. I like it.

Do you want this to also work for Llanowar Elves and/or Seething Song?

Also, the complicated way may not be the best way anyway. What's wrong with:

": Exile the top card of target opponent's library. If you exile a land this way, add one mana of any color."

I mean, the Obelisk is a mythic. Why are trying to restrict the color of mana it might produce?

Because then that can't activate that one insane card that just ahppens to be a mana ablity as a side effect of its huge effect...

A mana ability is an activated ability that creates mana or a triggered ability that triggers off of mana creation and makes more mana itself. So as far as I know Seething Song doesn't count. https://mtg.gamepedia.com/Mana_ability

My intent is to activate the activated abilities - hence the wording as I don't think it would even apply to triggered abilities since they aren't something you can 'activate'... if it works or could work that is. EDIT: The comprehensive rules speak of triggered abilities being activated so I added "activated [mana ability]" as a restriction.

This way it can activate the last ability of Ramos, Dragon Engine for example. This novelty is the most of its reason for being a mythic.