I dunno, some of Johns best prep schemes have been his 'long cons' where he can manipulate his friends and enemies to set the stage how he likes.
I mean, Ennis' run was John preparing the entire time for his confrontation with The First, and he succeeded because he had time to not only create a plan A (which involved screwing over Gabriel and getting him to fight for him) and the plan B which ultimately destroyed The First.
Same goes for Carey's run, where he was able to put all his players into position to destroy the Beast.
Tbf John's best chance here would be recruiting his few allies and associates who are still alive (generally his most powerful ones)- Swampy, Ellie, Map, Kid from BoM (Tim Hunter?), Zatanna etc
Even weirder there was literally a scene where Constantine tells Kit he loves this person more than he ever loved her, when really there hasn't been much showing that...
I don't see how anyone can actually call this battle. Let's take a closer look at the combatants.
John
1. He's the defiant Bugger who will never accept the control or limitations set before him. His whole MO is finding a back door or a window when he doesn't like the way to the front just because it's the only option presented. This makes him unpredictable as hell ( no pun intended). The few failings he has had he eventually finds a way to turn to victories ( no matter how many years it takes)
2. Most of John's prep (the majority anyway) is actually arbitrary prep he's done before an encounter for a rainy day. He's entered into many situations with no actual prep time and won because of stuff he had on standby.
3. His prep isn't just to do with tactics but simply knowing the rules of existence and playing the right hand at the right time, and knowing ( courtesy of his TP) the motivations and skeletons of everyone he needs to know of. For him it's as much about manipulating the individual to do what he wants, when he wants not
4. When he does actually prep for something specific he has several back ups on the plate should the first fail. There's always a plan e, F, and G (though he rarely get's past b)
Doom
1. He is the masterful tactician who usually only fails due to pride.
2. His knowledge of science and magic is almost without peer
3. he brings a lot of tech and power to the party
4.Though not as often and Constantine he does have some manipulation feats that match the best of John.
Now let's look at their best feats.
John
1. Convincing the supreme being to give him exactly what he wanted or suffer the consequences. Not a threat as "god" ( this was before he was called the presence) knew that what he said he would do John could and would achieve and found that option unacceptable.
2. Convinced the First of the Fallen ( it was never Lucifer that hated John it was a much older power) who hated him more than he had any other ever before and the other lords of hell to heal him and make him virtually immortal - the consequence if he wasn't was that hell would be destroyed by their own rules.
3. Made the Angel Gabriel his ***** to serve him as he liked
4. Killed the First of the Fallen and made him mortal ( later killed the mortal form and returned him to his immortal status)
Doom
1. Manipulated Reed to defeat the Marquis of Death.
2. Usurped the power of Pre retcon Beyonder
3. Usurped the power cosmic
4. Conquest of the microverse.
Where I find it get's interesting is the allies that they can call on for assistance as part of their prep. Both because of their arrogance and defiant natures have turned many a former ally against them ( or lost their faith). The thing is despite that John almost always has some form of leverage that he can bring to bare or some dept that is owed ( it's like he keeps and stockpiles them in droves) that he can use to bend the ones he want to serve him how he wants when he needs.
IMO opinion it's all going to come down to the length of prep time and how much contact or knowledge they get on the other. If the prep is limited to a week or couple of weeks I favor John because he always has some things "prepped" for every contingency. The longer the prep the more it favors Doom as their is more time for him to come up with plot like devices. The only combat John would have for these would be pulling in some of the higher powers he has in his pocket (which I don't know how sits within the rules. In many forums I attend this would be considered against the rules unless stated so in OP)
Similarly basic knowledge only favors john as the posts that suggest Doom would underestimate him would be correct. More intimate knowledge even though this also helps John to know Doom's motivations evens it out more as the manipulation edge would be lost to John
The poster who suggested time manip is just plain wrong, as this is equally on the cards for either to play. John is just as capable of using a spell for time travel. I'm also not sure if John's protection form death still exists. At one point he couldn't age etc.
Constantine wins, there are many demons who could try this 'time travelling' to kill him. Its not a joke to alter timeline ..like flashpoint. Still, Constantine will find not one but many ways to finish doom.
__________________ On Ignore list : GALAN007, tkitna