1 Eric Cartman from South Park and Porky from Earthbound
2 Light Yagami from Death Note and Justin Bieber
Justin Bieber's double from The X Factor UK his name is Luke Lucas...he is not famous like Justin so do not confuse them. Possibly similar ages.
3 Mario from Super Mario Bros and Joseph Stalin
I so agree. They're nothing alike.
4 The Joker from Batman and Kefka Palazzo from Final Fantasy
At least they're both fictional villains, man. It's not as bad as crossing over Sephiroth with Karel from Fire Emblem, because Karel is one of the good guys in FE and not a villain like Sephiroth is.
5 The Doctor from Doctor Who and The Doctor from Cave Story
6 Solid and Solidus Snake from Metal Gear Solid
7 Happy Tree Friends Lammy and the original Jammer Lammy
8 Original Pocket Tales Conker and Bad Fur Day Conker
They're the same character, just different games.
9 Superman and Bizarro
10 Mettaton from Undertale and David Bowie
The Contenders
11 Simba from The Lion King and Ike from Fire Emblem
A DeviantArt user under the name Soraheartsforme made a Death Battle between Simba and Ike which (in my opinion) is a bad idea for a crossover. Not cool, man. (Prays that Ike wins...)
12 Elh Melizee from Solatorobo and Zuri from The Lion Guard
13 Star from Balto and Ed from The Lion King
14 Batman from DC and Iron Man from Marvel
15 Sora from Kingdom Hearts and Pit from Kid Icarus
16 Prince and Michael Jackson
17 Ansem from Kingdom Hearts and Karel from Fire Emblem
18 Scar from The Lion King and Karel from Fire Emblem
19 Rainbow Dash from My Little Pony and Fuli from The Lion Guard
I hate Fuli so much. It seems that not every franchise is safe from awful crossovers with TLK, not even MLP I'm afraid.
20 Yak from Balto II and Janja from The Lion Guard
21 Kaltag from Balto and Shenzi from The Lion King
22 Nikki from Balto and Banzai from The Lion King
23 Miles "Tails" Prower and Scrappy Doo
Again, Tails is not annoying and comparing him to the most annoying side characters in fiction is not right. Hopefully, Tails' comeback as a playable character in Sonic Mania will help him get the positive reception he deserves.
I hate Scrappy so much. He's annoying. Tails is just awesome.
24 Beshte from The Lion Guard and Murray from Sly Cooper
25 Ono from The Lion Guard and Reyson from Fire Emblem