The Ancient Magus' Bride: Jack Flash and the Faerie Case Files (Werewolf Transformation)

 Volume one of this manga introduces Larry, the werewolf sidekick to the titular heroine.

Sometimes Larry absentmindedly shifts between his two forms: 

 

A little bit of muzzle growth:

 

And here's a spread from the start of the book showing him in mid-form:

 

Monster Raban (Kaiju/Lizard Monster Transformation)

Thanks to Dinonator for recommending this manga from 1958. A scientist comes across his rival, who has been reduced to skin and bones by poison, and injects him with a vial of Godzilla's blood, hoping it will be lethal. Instead it turns his rival into a giant lizard.  

 

The Werewolf Who Wants to Stay Alive (Werewolf Transformation)

Volume one of this manga (Ikita gari no Werewolf, 生きたがりの人狼) has lycanthropic action in its first chapter:

In the second chapter the good werewolf meets a bad werewolf, and they begin a fight to the death. Keep in mind that the blond human (the central character) turns into a dark-furred werewolf who is good, while the dark-haired human turns into a light-furred werewolf who is evil.

Zenki and Togekichi (Tiger Transformation)

"Zenki and Togekichi: The Tale of Climbing Dragon Hill" was a one-shot manga published in Jump GIGA (Winter 2021).

Synopsis: "Childhood friends Zenki and Togekichi take on the mystery of a mysterious slope that never goes downhill. Several former human beastmen appear on the mysterious slope, and the protagonist, Zenki, also transforms into a tiger-like beastman as he climbs the slope."

There's also a reproduction of the comic on YouTube with a voice cast, but it's all in Japanese.

Violence Jack (Werewolf Transformations)

My thanks to Imitater on our Discord channel for finding this scene from Violence Jack (vol. 5, chapter 1, "Evil Town Part 2"). It involves murder, rape, and nudity, and is thus NSFW!

The horror starts when a group of thugs turn into werewolves while forcing themselves on a several women:

 

One of them reverts after getting scared:

 

Then Violence Jack barges in and proceeds to murder the werewolves, who either revert before running away or after getting killed:

This chapter was faithfully adapted into anime, except the werewolves! Apparently rape and slicing people in half was okay but nobody wanted to draw transformation scenes.