Eventually you are going to want to trade with Mongeese, or I kill you. When you do, I kill you...
Sorry. "Eventually" doesn't work here. If it's better for me to not attack because I will lose a creature, I won't attack. Same goes for you: If you attack I won't block and attack you back with 4 damage, so I think you won't attack either.
I've seen 5CB rules stating that, while discard such as this does work against its user, it still happens- the card that's best for the opponent will be discarded. Is this the case for 3CB?
Yeap. Discard occurs with what's best for the opponent.
Anyway, how do you get a WW?
Assuming I'm playing first, I'll play my land, then I assume you play your creature, then I'll play one of mine. You'll then play Sphere and won't attack
after that and neither me ('cause we would lose our only creature).
Note: I skipped Hexmage and Skirge because that deck didn't count for the "continuity" of the game.