People keep calling this land broken. To me it seems like a tweak on the Karoos like Boros Garrison. Are there any Shamans it's particularly crazy with?

Perhaps surprisingly, there don't seem to be any Shamans with a ability, so you've dodged that one.

Despite the Karoo drawback, this is simply too good to print. Even tapping for a single mana is extremely good with the second ability.

Really? But most (well, many) Shamans tap for mana or something anyway...

I think only research on the shamans would show if this card is broken or not, as of right now i dont see it broken but i do see the potential for it to be completely broken, fast mana is really dangerous, and as a karoo its cool, but being able to untap it multiple times is where it starts to get dangerous, i say until someone finds a way to break it you could keep it like that, but mostly tribal lands and cards in general that are have the potential to be so good, aren't common, i'd say uncommon would be proper.

Hm. The rest of the tribal cycle (white = artifacts = Museary Gateway, blue = instants = Fleeting Whispersilk, black = sorcery = Cloak in Terror, green = enchantment = Verdant Abundance) are commons though. So I think I'd like to find a different common design for a Tribal Land - Shaman if this one is problematic.