Doubling up on proliferate triggers can let counter-based strategies spiral out of control fast, buffing your creatures and planeswalkers while dishing out more poison counters to your opponents, if you go that route
A creature with a shield counter on it may still be destroyed by state-based actions if it has damage marked on it equal to its toughness or has been dealt unpreventable damage by a source with deathtouch
Should you fill up your yard sufficiently Jace will flip and cease being a discard outlet
You can also use this reactively to answer mass or targeted removal too
No, not Bitterblossom, but rather exceptional flexibility in the role it takes on in a given matchup
For the last step, however, The True Scriptures goes all out, reviving all creatures from all graveyards under your control