Final answer:
The item in 'The Binding of Isaac' with +0.5 Damage Up, a 1.5 times Damage Multiplier, and tear knockback effect, previously named 'Max's Head', is now known as Cricket's Head.
Step-by-step explanation:
The item in question from the game The Binding of Isaac that provides the effects of +0.5 Damage Up, a 50% or 1.5 times Damage Multiplier (which notably does not stack with the Magic Mushroom multiplier), and adds significant knockback to tears without increasing the shot speed stat is Cricket's Head. This item was indeed previously known as 'Max's Head' in the original game before being renamed for the Rebirth edition. It can typically be found in golden chests within the game.