The effects of the super serum. We first see it violently injected into a bunny who turns into a purple hulk monster, then attacks a scientist, with strong implications that the scientist was killed, and destroys the camera filming the experiment. Then there's the reveal of the serum-infected minions...whilst they are Nightmare Retardant all the way, it's a little disconcerting to see cute little corn kernels turned into violent Omnicidal Maniacs stuffed in cages and gnawing at the bars.
Speaking of which, there's a brief bit in the climax when Gru and two of the normal Minions are climbing to the roof to get away from a swarm of Brainwashed and Crazy Minions. They end up cornered by them, no way out...and when the camera cuts to the swarm, there's a Minion in front licking its lips. Earlier we saw that the purple ones would and could eat anything, so it's pretty strongly implied that they were going toeattheir former boss.
Not to mention the part where the purple minions are chasing them through the building. The way they surged around corners and climbed on each other to raech the roof evoked World War Z to some viewers. (Which - according to the directors' commentary - was exactly what they were going for.)
Prior to Gru and two of the normal minions being chased, one of the evil Minions sounding the alert on them with a screech and pointing at them a la Invasion of the Body Snatchers when they discover that the normal minions are wearing purple paint in order to blend in.
What about Antonio? The kid may be Kid A Nova and broke Margo's heart, but he's still a kid. His dad definitely got arrested and his mother was never seen or mentioned by him or Eduardo. So, the question remains: Does Antonio go live with his unseen mother or does he go live in a orphanage?