Edit- this turned out pretty long. Lol
Is this Johan from Monster?
I think instead of one of em beating the all others what i guess most users here are imagining , this situation will be much more complex than that. These characters will take each other and the one playing safe in the end would end up surviving. Another key point here is, they ain't aware of each other abilities at the start of the game, since they have no info on each other which imo is most crucial step in the process of taking one out.
Now i haven't read Dungeon Defense so i really can't comment on him.
Starting with Light, his main con is he requires name n face of the user to kill and relied on TV to get his targets in Deathnote . Since be it L, Johan or Lelouch he isn't gonna to get those names n faces easily(L keeps his identity n name hidden, Lelouch wears a mask and Johan doesn't commit the crime himself, more name n origins also mystery to solve) , which would force him to come out n get close/in touch with his targets which isn't a good step given the risks.
Bt yes if he blackmails or manipulate allies into writing their names in the Death note paper like he did with detective in the metro at start would be his biggest plus here. (this potentially pose danger to Lelouch given his identity(face) is known to their family members given Light figures out his name n heads out to meet his sister/other family members or friends. As for Johan even tho his face is known by his sister n persons he interacted with in the past, his name was a mystery until the very end if i remember correctly:unsure:)
Light further has one trump card, he can give his half his life in exchange for knowing names(even tho we all know he would never do that), if we include that he would gain quite an advantage here, especially against L n Johan.
Bt like i said he has one big flaw he is overconfident.
Lelouch keeps the masks on, so even tho his name might get figured out it would require physical force to get his maks off in person with Police or forces help, which is still hard job to do given his cunning nature and that he can literally manipulate anyone with his eyes. Others are most surceptible against him, if they end up meeting him without being aware of his abilities. His abilities can be beneficial against L, given he can manipulate detective into Killing L or also Light if he hides amongst em pretending to be solving cases. Against Johan i dont think its easy to attmpt this(unless direct confrontation) given his continuous random movements and unknown whereabouts, and that he kills without second thoughts so can't really expect few person to be successful in attempting a kill.
I think only Light stands a chance at takin him out by contacting Lelouch family members, it would be hard for police forces to tackle Lelouch and same for Johan with mass manipulation. Bt one can still Manipulate other to kill other, if that make any sense lol. I would get back to it when i get to L.
Johan, is psychologically the most dangerous amongst em, he is true Evil .The fact that he can easily manipulate masses to go on Kill mode, is a fearsome ability to imagine especially against someone like L, who works with the help of masses, police n detective, and any one of can go Nuclear on L. Or Light if he comes out and hide among the detective while pretending to be helping in their case. Against Lelouch, this ability won't work tho, i think Lelouch manipulation is stronger superhuman ability.
Johan negative point here is that we don't know how he would fare against the level of Intelligence of World best detective like L, in Monster It was a simple Dr that was chasing after him and he neither had the training, Proficiency or manpower to do that detective stuff properly . While L should be able to easily do that stuff given he has manpower, brains, access to information as the Best detective of the World.
In the end i would say my best Bet here is L, he is the best Detective out there in the world. And even tho he supposedly lost to Light in Deathnote, bt if one gauge the odds that were against him from the very start, he made much more progression in comparison.
Light only survived against L because L had to work within following in the general rules of society and had great advantage of Death note and anonymous identity from start. L has to figure out Light from among the countless people on Earth and it wouldn't be wrong to say he was successful in that. Not only he easily got aware of some strange abilities in work for mysterious death, he easily also figure out Light abilities n process of Killin. Imagine the same with Lelouch n Johan.
Figuring out opponent abilities is like wining half the battle in itself. That would help L take the necessary step and actions to ensure his safety.
Now keeping himself from harm way, he can start figuring out the identities n origin of these characters, and comparable to finding Light among billions of people) especially given Kirra can kill anyone simply from anywhere just with name n a face) and hnce Lelouch n Johan case doesn't seem impossible.
And once he is aware of Lelouch n johan identities, the very first step he can take is reveal their identies to the world, where he would be in the position of making these 3 face each other off while keeping himself from harm way.
And in the process he can also gain more valuable information about em, which would again help him take em later on. I can easily imagine Light going after Lelouch one of the family members to take our Lelouch. As for Johan, i don't think capturing with manforces is really hard to do given he is human at the end of day(very fact he would have died with bullet in the head if not for Dr in the very start) and can't instantly manipulate people to successfully escape . His abilities are more concerned with takin benefit of evils/doubts inside humans and forcing the negativity out to turn em hostile or by blackmailing em into killing.
But If to really stand a chances at winning this L, has to play with no rules or followeing no Laws of modern society. Johan needs to b killed as soon as he is captured else it would be impossible to keep him captive. Same for Lelouch.
Also L would have also won against Light if he had killed him the moment he grew suspicious of him.
Now if Light had taken out Lelouch, this battle would be btween L n Light n if L plays with no rules he wins.. N if Light do the eye deal he wins.
If Light fails to take out lelouch(less likely tho given Light could ward off L for such long time he is master genis when it comes to it) bt if Lelouch catches him first, Lelouch now would be formidable enemy for L, given he now also has Death note in his profession. Now it would dpnd on if Police forces/manpower will be able to capture Lelouch or not, given Lelouch has his Robit like machine and he can manipulate em with his ability.
Now having written this, i feel i went with one way approach i might arrive at different answer is i start with different start. There are other individual aspect that i failed to consider in this hypothesis. Bt my main focus was i give more edge to L n Light when it comes to Brains. The amount of thought process that went through their heads in makin plans to outdo each other with multiple step moves with chess pieces in Chess i dont imagine Lelouch n Johan keeping up with that. Lelouch while had his similar moment of moving chess pieces like on chessboard in the very starting of fights bt his talent lies on doing the best in the situation (at least that's what i remember, it's been long i watched it) and JOHAN in manipulative the evils inside us. Hence i naturally favour L n Light for their deep thought process.
Fun fact- (what if situation to consider)Lol what if Johan gets possession of Death note by beating L, man that would be sick combination.