There was almost no fill in during the 5 year jump outside of Aqualad and the Superboy/MM breakup. Somehow dude proved himself capable as some kind of coordinator/secretary.
Like how did Gars martian blood transfusion give him animal shape-shifting abiliaies? How did Bumblebee get her powers?. ...and best believe S3 will have another jump.
I got that but there should be a reason why he turned permanently green and can only turn into animals. Just gotta chalk it up to comic book reasons,
The animal transformations I say because him and him mom were heavy into animal care and etc.. its probably subconscious.
Bumblebee is a protégé of Atom so somehow .. maybe during college or an internship she worked with him... Remember in s1 Bumble and Mal were in HS with MM and them.
If you check askgreg he probably answered the BB questions unless its spoilers
edit: it was asked
Billy Black writes...
Will for centiers or die withe the team Does Garfield a longer lifespan after becoming beast boy because he has misss marshin dna
Greg responds...
I'm sorry. I'm not entirely clear on what you're asking... but if you're asking if Garfield will live longer than the average human, the short answer is ... it's unknown. He's an anomaly.
Response recorded on February 13, 2014
Question received on Fri, December 06, 2013 12:54:18 PM
Chad writes...
What year did garfied become full green and what year did he join the team and how did team know marie was dead
Greg responds...
SPOILER REQUESTS.
JJ writes...
Hey greg. Quick questions:
3. Can Beast Boy shift into people like Miss.M or is he limited to animals.
Greg responds...
3. Animals.
we'll see.
. Vandal ran shyt man
(I've watched season 1) 
I'm ready for a new season.