It came from the Toy Chest: Hamato Yoshi or Hamato Yoshi's pet rat.

 It depends on continuity. In any case everything else about Splinter is trains the Turtles to avenge Yoshi. Take the names from a Renaissance art book. mentor, father, sensei... he taught them to be ninja teens. He's a radical rat, yeah!

Splinter: She-Ra! Where's my god-damned tea!?
He-Man: Did he just call me She-Ra?
Raphael: Did he just make a Final Fantasy VII reference?

Articulation 
Splinter got the shaft here. He Has Articulation but some of it is hindered by his robes or by posing limitations. The plastic robe hinders the awkward torso articulation. The leg articulation is hindered by Splinter's inability to stand properly. More often than not, the tail will act as a third leg.
3.5

Splinter: If I don't get my god-damned tea, Imm'a cut a bitch!
Shredder: Did he just call me a bitch?

Paint and sculpt 
He lools like his vintage self, only bigger. The only "weird thing" is how none of his tunics match the vintage figure. The cloth tunic is not shaped like the Vintage one and has a different stretchy band belt. The soft plastic tunic looks closer to the vintage toy when closed but the belt has loops, which is wrong for the kimono that Splinter is wearing.  they look good but they are inaccurate.
4.5

Splinter: WHERE IS MY GOD-DAMNED TEA!!
Rocksteady: I dunno.
Splinter: GIVE ME MY TEA OR I'LL GO
KATNISS EVERDEEN ON YOUR ASS SO HARD
THAT I'LL MAKE AN ACE VENTURA 2 REFERENCE
OUT OF YOU!!

Accessories
Splinter has:
Bow
Arrows
Shuriken
Cane Sword
These are repeated in the brown vintage rack
Extra hands
Plastic tunic
A Normal cane
Cup of coffee or Tea.
Pre-Mutated Turtle
He definitely comes with plenty of stuff.
5.0

Splinter: Finally, some good tea...
Mako Splinter: Sharing tea with a fascinating stranger
is one of life's true delights!
Splinter: Just because you're very handsome, and have the voice of an angel, doesn't mean that I'm sharing my tea with you!
Mako Splinter: Stay, safe, friend... Come, Prince Zuko, we are not
welcome here.
Turtle Zuko: Honor? Honor... Honor!

Overall
Splinter gets a 4.33 as his final score. The articulation and inaccuracies on the robes kinda ruined it for him. I kinda wished he had gotten a second head because, I don't like the vintage toy head. I'm ALMOST tempted to paint pupils on my Splinter. If he had a headband covering his eyes, the lack of pupils wouldn't bother me. I sharpied the western belt loop to hide its Westernness until I can buy a black ribbon to use as a Martial arts belt.

Splinter: This God-damned tea makes me
feel like a man-child's plaything!!