I despise the “Beast” mode mutation of Unit 02 in Rebuild of Evangelion for two reasons.
Number 1: Mari Makinami is a terrible fanservicey God-moding Mary Sue and her managing to hyper-synch Unit 02 into a new battle format is duly unacceptable because A). attempts by outsiders to enter an EVA with a predilection for particular pilots are often met with violent loss of control, and B). Synch levels of the intensity which are required for Beast Mode cause dissolution of the pilot into the EVA.
Number 2: If there’s an EVA destined for form mutation, it’s the Mass Production Unit.
But Anno introduced Mari to ruin the series anyways, so it’s okay.