OK,so...you do mean Baxter! Well, this is my problem : i always point out the bad things and the good things BUT everybody complaint when i point out the bad and when i point out the good,they tell me that not everything is good!!! X | =_= Let's start, we all have a "evil side",i know,it's just that...if we think of Mike or Raph,they're good guys (i can't say the same of Leo,but that's other theme) but Don,he accumulates grudges,that's the bad side,i know he fight to don't give in to his "demons" and that's the good side. Now, some examples of poor evil Donnie :
1987 serie episode :"Donatello's duplicated" Well,here his duplicated was IMPROVED was NOT a EVIL CLON just improved,ALTHOUGH,he wanted to CONQUER AND THE WORLD,can you explain me that,please???.
1987 serie episode : "Night of the Dark Turtle".here did NOT changed personality,he just "drew his resentment" with Shredder and he "broke" and nothing more... but just because he is patient,he hadn't done anything...yet.
2003 serie episode:...(i can´t remember) but all the seventh season he was angry (about Splinter,of course,and his brothers were irresponsable,but REALLY MAD)
2003 serie : "donatello's clon" do you remember that guy? Oh,i bet yes! well he's just his "evil side" and he has the same personality as his 1987 clon. Curious,doesn't it?
2012 serie episode :"Heart of Evil" and "I Think his name is Baxter Stockman" (in the trivia of Donatello say this : "Due to his behavior in I Think His Name is Baxter Stockman (and various other episodes), he is the second to Raphael in temper and anger."
Image comics : "Don-cyborg" (He scared me) He even almost fight with Leonardo.
Mirage Studios : your example and many (MANY) things. Anyways, he didn't wanna kill Skonk (from C.R.A.P. from "Survivalists) And i feel that he's "mysterious" and serious,just that.
IDW comics : "Metal-Don" (poor) actually, i don't know a lot of IDW... i haven't read it :V i begining with Archie Comics but i'll do it ¡i can assure it to you!!
By last : MNT Gaiden i already know that comic...¡it's wonderful! ¡i LOVE it! however... i'm SORRY for him,he i pity him :( many say he's gonna die or something like that but i DON'T think that *sigh* i'm glad you think it's not irremediable.
And i don't think Mike has become evil or vegeful