Wow. Very interesting mechanic in black. It'd more normally be seen in green or white, but if this set has Curses or similar then it's somewhat plausible in black. I'd expect it to be uncommon rather than common though (especially as it's bypassing mana cost: turn 1 cast whatever the set's 1-mana discard spell is to discard Omniscience, turn 2 Bloodthrone Vampire, turn 3 this and win?)
Also note that an equip cost of means it's quite easy to sling this between creatures. For you can grant two creatures landwalk before declaring attackers.
Wow. Very interesting mechanic in black. It'd more normally be seen in green or white, but if this set has Curses or similar then it's somewhat plausible in black. I'd expect it to be uncommon rather than common though (especially as it's bypassing mana cost: turn 1 cast whatever the set's 1-mana discard spell is to discard Omniscience, turn 2 Bloodthrone Vampire, turn 3 this and win?)
Fascinating tweak on Firebreathing. Uncommon is the right rarity for it, and
feels like about the right cost.
Also note that an equip cost of
means it's quite easy to sling this between creatures. For 
you can grant two creatures landwalk before declaring attackers.
I think the way to do it is:
> Equipped creature has "
: Choose a land type. This creature gains landwalk of the chosen type [until end of turn?]."
You don't need to target a land an opponent controls because, well, that's the only reason you'd be doing it...
If you're happy to neglect the very few ways to attach Equipment to opponents' creatures, you could simplify this further to:
>
: Choose a land type. Equipped creature gains landwalk of the chosen type [until end of turn?].
Wow. Yeah, an interesting tweak on Oust mixed with the occasionally-seen white taxing mechanic. Nice.
I like this.
The wording bothers me, but when I look at existing Magic cards, it makes me think it's right.
Please help with the wording