As the endgame Summoner set, it would make sense that it would give bonuses to both regular minions and sentries. I think the amount of extra sentry slots should be the same as minions, so 5 extra sentries.
All boss and enemy life/damage/defense increased by Graham's Number to the power of a Googolplexian times TREE(3).
Bosses don't drop anything besides a special Lifeless Mode-exclusive item, which always negatively impact the player.
King Slime - Unroyal Gel - King Slimes spawn...