So,here's some reason's why I head canon EthGoesBOOM's Puppet as having ADHD and Autism

Rejection Sensitive Dysphoria:
In Eth's gameplay for FNAF 2,Night 6,he's shown crying and freaking out over the fact that him and the other Toy Animatronics are gonna be scrapped. Since thus is basically being considered a failure by the company,and how people with RSD want to avoid being seen as a failure,it makes sense he would freak out how he does.

Impulsivity:
....I think this one is obvious. Still,for those who don't get it,he acts on impulse very often,and sometimes,it's the main focus of the episode.

Executive Dysfunction:
His game Mechanic in FNaF 2 and UCN. He definitely WANTS to attack the guard,but can't due to Executive Dysfunction.

Object Permanence Issues:
Once he gets distracted by something,he tends to forget it exists. This is shown by how he basically forgot Springtrap existed before the FNaF 3 arc,judging by the fact that Puppet died to Springtrap.

Hyperfocus:
Going off my last point,he tends to focus  on thing a little bit too much,being very obsessed with giving life to things. This also might be an Autistic Special Interest,but we'll cross that bridge when we get there.

Hyperactivity:
.....Do I need to explain this one too? For those who don't know,the Puppet is always shown to be full of energy,and definitely shows it by how loud and rambunctious he tends to be.

Understimulation:
This,along with a few things I'll say for the Autism Symptoms,might be a reason he attacks the Nightguard when his music box stops playing. It's giving him sensory input in another wise baren environment. He gets bored without it,and thus,he attacks the Nightguard.

Now,for the Autism Symptoms he displays:

Meltdowns:
Hooo boy,does he ever! First of all,his Night 6 Meltdown is the classic Meltdown. However,he also shows a different type as well. The violent type. As I said for Understimulation,he needs that music box to give him sensory input. If overstimulation can give a person a Meltdown,then understimulation can too. He,instead of his usual type of Meltdown,goes for the violent type. (Duh)

Schedule Obsession:
Well,how he gives life definitely might be part of it,since he doesn't seem to do it on holidays. Another thing,what I said before. Breaking of a Schedule might have flung Puppet for a loop. (You're supposed to play the music box from midnight to 6 am)

Special Interest:
Well,it's giving life,definitely. He's shown to be obsessed with the Idea.

Hyperfixation:
My last point,but only for a short period of time. His Popgoes Story just makes the biggest sense to me for being a Hyperfixation of his,since it was only a one off thing.

Stimming:
His music box is probably how,and yes,listening/creating music is a valid form of stimming. He probably likes his music box as much as he does because he uses it to stim and avoid Meltdowns due to overstimulation.

Attachment to inanimate objects:
......Do I need to explain this one? Seriously,he gets so attached to them he literally brings them to life!

Thank you for coming to my TedTalk. /j

No,seriously,thank you.