So, one of the signature DMC series features is Devil Trigger (デビルトリガー debirutorigā), the ability to use demonic powers, main of which is the ability to transform to Devil Form (魔人 majin). The amount of DT powers is measured by synonymous gauge and it's activated by synonymous button.
Devil (demon) form (魔人 majin or 魔人化 majin-ka) is a demonic appearance (of someone or something that has other appearance), this term has been used in japanese versions since DMC1, notwithstanding the change of majin concept from Devil Arm-based in DMC1 to character-based in DMC2 onwards (from majin Alastor, majin Ifrit to majin Dante, Vergil, Nero and so on). So Angelo Credo and Sanctus Diabolica is majin Credo and Sanctus respectively. Reason why western versions use Devil Trigger term for this instead are unknown but understandable - it's a basic DT ability so why not. Things got a little complicated as DMC2 came out.
True Devil form (真魔人 shin majin) DMC2 had two Devil Trigger modes: Devil Mode (魔人モード majin mōdo) and Ultimate Devil mode (真魔人モード shin majin mōdo) - the latter is activated when Dante triggers with health in red zone. Literal translation of 真 is true, but japanese Official Complete Guide by Capcom and Studio Bent Stuff uses ultimate. The mode itself is clearly inspired by DMC1 Sparda's Devil form (mission 22). It uses DT gauge, has its own movelist and is not affected by Amulet Devil Hearts. And of course majin and shin majin have drastically different appearance. The game itself doesn't explain shin majin neither from in-universe perspective, nor gameplay-wise (tbh this game barely explains anything - but it was a troubled production), neither does game manual and many players don't even know about its existence. Hideaki Itsuno was really fond of this form (as stated in 3142 interview) and sought to bring it back in DMC4. It didn't happened but one can see concept art for this iteration in Devil's Material Collection artbook, and subsequently in 3142. But it did came back in DMC5 for both Dante and Vergil with new story explanation and english name. Sort of.
Sin Devil Trigger (シンデビルトリガー shindebirutorigā) In DMC5 Dante gets his shin majin after fusing Rebellion and Sparda into new Sword Dante (not sure about Vergil's circumstances - Nico's file hints it has to do with Urizen eating the fruit or something). This mode retains inability to manually cancel out of it as DMC2's UDM, but Dante (and Vergil) hold actual weapons in their hands, as previous iterations used built-in weapons (light swords in DMC2, tail in DMC4 concepts, but one may argue that DSD is actually Dante's built-in weapon). And it uses dedicated gauge - the SDT gauge, which is charged from DT gauge. As I mentioned earlier western releases tend to use the word Trigger instead of Form, but Sin part is still a mystery, as game doesn't explain what's so sinful about it. The only reason for this I can think of is that Japanese version interface is built upon english interface and they needed homophone english word for it to not confuse japanese players (I believe moves like Sin Stinger and Sin Inferno is still spelled with 真). And I'm pretty sure the reason Sin Scissors got promoted to Death Scissors is because Sin is being associated with SDT. I have more questions to english localisation, but now it is how it is.
The lack of proper explanation of shin majin in DMC2 led to some unofficial names popping up.
- The only (to my knowledge) licensed english language DMC2 guide - Bradygames Official Strategy Guide by Dan Birlew devotes to shin majin a single paragraph at the end of the book and calls it Super Morph, that same guide calls Million Stab move the Sashimi, so I think we can easily discard it.
- Term Desperation Devil Trigger was coined by players describing circumstances in which it activates, it even made it's way to Wikipedia.
- I tried to find the source on usage of Majin Form for shin majin but I couldn't. It started to appear some 10 years ago and is fairly nonsensical - did someone overheard it badly or copypasted hastily and missed first four letters?
- Term Perfect Devil Trigger must've been some fan translation of 真魔人 by someone who had access to DMC4 Devil's Material Collection, but eponymous article is mixing up two discarded DMC4 concepts - Dante's shin majin which would be used in addition to existing form and Nero's majin which would be used instead of form appearing in the released game.
- The only development material book translated to english Devil May Cry: 3142 Graphic Arts was published by Udon Entertainment and - they had one job! - shin majin is translated there as Ultimate Devil Trigger in DMC4 part and as Majin Form in DMC2 part. I wonder if they were referencing this very wiki.
So I think shin majin as a single concept deserves its own article, reflecting its evolution in the series. What would admins suggest? What name to use for the merged article if we do merge them, should we rename existing ones, dump it all to Devil Trigger or just leave it like it is?