Man-Thing (Plant Monster Transformation and Pig Reversion)

Our thanks to the anonymous commenter who recommend the 2017 Man-Thing comic miniseries, written by R.L. Stine. From issue #1:

The cover of issue #2:

From issue #3, a trippy sequence involving a pig-to-human reversion: 

Le Reveil du Zelphire (Tree and Monster Transformations)

Sylvan, the appropriately named protagonist of this French comic, has the ability to turn into an anthropomorphic tree. From volume one:

Later on...

And in the climax...

 

Volume two opens with an interesting reversion scene and also has a TF scene at the climax:

 

In volume three the villain undergoes an operation and turns into a giant hideous monster. The heroes escape on an airship that falls prey to the monster:

Spider-Man: Curse of the Man-Thing (Lizard and Plant Transformations)

In the first issue the Lizard and Man-Thing meet in their human forms (they're both scientists). The Lizard transforms, and then during a fire-fight the Man-Thing germinates from some plant matter.