De Killer

Okay so let's just go over all the bullshit De Killer does in Investigations 2 here.

The whole premise behind his actions in this game is that he was hired to assassinate the president of Zheng Fa by Simon Keyes. It turns out the president was actually a body double and now De Killer wants to kill Simon for not informing him of this.

Okay first off who gives a shit if the president is actually a body double? His whole reason for turning on Matt in 2-4 is that the man was straight out conspiring against him - he recorded De Killer kill Juan so he could blackmail him into being his dog. This is so much pettier.
Second is how could he be so sure that Simon lied and just, didn't know. Something like this isn't going to be common knowledge; not even the president's guards knew. How's this clown from the Berry Big Circus gonna know a scandalous secret like that?

Not only that, but he shows up in both I2-4 and I2-5 a couple of times for no reason other than to remind Edgeworth that THE TRUTH HAS NOT YET BEEN FOUND...

1: Fuck off, you're just here to be annoying
2: Why do you even need Edgeworth to find the truth for you lmao just go down to the circus, kill the guy and call it a day
3: Why are you even appearing before him in person, isn't that kinda a really stupid idea?

Aside from all this stupid shit the way he's portrayed is just a lot sillier than in Justice for All? Like he goes from this genuinely ominous figure to, busting into a president's airplane twice (once with a hostage at gunpoint), getting his ass kicked by a bodyguard, teleporting outta the circus... it's minor stuff in comparison and it's really just showing him in a different context if you wanna go that route but it's a lot harder to take him seriously like this - and, given that final scene in the circus, I'm pretty sure the game wants us to take him very, very seriously.