As for the fourth pack, it will just bring your deck up to 66 cards but wont introduce any new card types
6 Assemble The Players Now That You're All Here Sometimes the little creatures need an advocate for them in your decks and with Assemble the Players, you get a fantastic engine to keep casting as many spells as you can
While he does cost a steep 6 mana to cast, he also comes with an ETB tutor trigger, and if it's Hammer of Nazahn he even saves you the mana to cast it
If you have ways to mill your opponents, Memory Plunder gets better and better, and in general, I feel like most Dimir decks should be finding room for this spell
Accumulate Wisdom become peerless card draw, Combustion Technique is efficient removal, and Gran-Gran makes all your non-creature spells (which in this deck is pretty much everything) cheaper to cast