Changed the equip from to casting an instant or sorcery spell.

Whee. Casting a spell as a cost is a very wacky mechanic, but I believe it works. SadisticMystic thought it worked on his Kite-Mount Raven, and his understanding of the rules is second to absolutely nobody else I know (including anyone at WotC).

Amusingly, this turns Leonin Shikari into a Vedalken Orrery for your sorceries.

Yeah, I'm pretty sure you can do this, but it would also work with a Cranial Plating style workaround where a triggered ability equips it, so that's the backup.

Also, nice find with the cat, do you happen to know if the rules allow equipping an equipment to a creature which already is equipped with it? That way all you need is the Leonin and you have a free upgrade to all your sorceries.

The rules do indeed allow activating the equip ability, as long as the creature can be targeted. (So you can't go infinite with Lightning Greaves+Daru Spiritualist unless you have another creature.) Technically the equipment doesn't move (which doesn't matter much, but matters with things like Grafted Wargear).

Are we sure this doesn't do crazy things, like let you cast Decree of Savagery for free? I'd think it would work a bit better if this said "When you cast an instant or sorcery"... but that's just one man's opinion.

There is a difference between an instruction to "cast a spell" (Havengul Lich) and an instruction to do so "without paying its mana cost" (Counterlash). Several cards already tell you to cast a spell during the resolution of some effect, a timing abnormality because you don't have priority at that time; the only difference here is that the timing is moved up into the window of paying costs.

@Alex:

I just meant like can you equip an equipment to a creature it's already attached to? I'm guessing no, but I don't know for sure.

@SadisticMystic:

So the timing's okay right? Because having no equip cost and just saying that you equip when playing an instant or sorcery is tempting, but seriously adds to board complexity because you can equip at instant speed. As I have it here I believe that since I'm actually using the Equip keyword then the clause saying 'Equip only as a sorcery' still limits the player to equiping during their own turn, even when playing instants.