Against green, Wrath of God will often suffice
Enchanted cards are not guaranteed in any specific position within a pack
A creature or planeswalker on your opponent's side is gone just by casting 3 black mana, then you can turn around and exile this creature to get a Zombie token in return
Well, well find out in Kate Elliots The Wildered Quest ebook, which will follow Rowan Kenrith (see below) and set the stage for Throne of Eldraines story
As to when to stop torturing our aquatic friend, once you average turn 3 kills over a reasonably-sized number of games (or simply once you feel comfortable you wont miss these plays when also having to consider your opponents options), you should be ready to move on to playing actual games
For flavor reasons, and to start pushing into a new space, we made these enchantment tokens