They're equally satisfied by an artifact you sacrificed to pay a cost, a creature you controlled that was destroyed by Murder, or an enchantment you returned to your hand with Leave in the Dust
Did you kill or exile him
The reason you might do this is simply that you get a bit more bang for your buck in terms of your spell becoming purely removal rather than a modal removal/reach card
A: It's kind of a weird thing to give up, to be honest, but if you're familiar with the old card Rock Jockey, it'll help
If an ability of the equipped creature states that it has flying "as long as" a condition is true, that condition becoming true won't cause the creature to gain flying
For the purposes of this list, Im sticking to cards in greens color identity, so every green card here is fine with your mono-green commander in EDH