Am I the only one who was disappointed Mega Evolution was simply a consequence-free upgrade to qualifying Pokemon? In shounen manga powerups like this always have some drawback:
>kaioken: destroys the body
>spiral energy: makes blackholes
>Gear 2: shortens lifespan
>nen vows: ages you or worse
>synchro summon: summons robot apocalypse
Even Battle Bond, was tied to its trainers stamina, with Ash taking hits along with Greninja.
The ultimate weapon's origins came close, hinting that Pokemon are draining their trainers life force to Mega Evolve, but that wasn't explicitly said. As of SM it's consequence free, soylent green is beans