Originally Posted by Tyger7
Well I did mention that in the achievement description, that only the person playing as Totec will get the achievement!
Since it's not technically a cooperative move, he does it by himself. I guess people are reading it wrong.
It looks pretty clear to me. Play through the first level SOLO with both controllers/accounts seems easy. Then get that return to sender in co-op at the start of the 2nd level. Great job on the guide. The collectable will take awhile...