Like Plastic Man or Mr. Fantastic.

The first thing that comes to mind is shape_shifter. There may be a better term.

I also tried to find out what tag to be used for that. Searched for *mold* and *clay* but couldn't find or think of anything else.I went for moulded_penis as a joke/last resort tag for post #1094717 but it has been removed. Still have no clue what actual tag I should be using

Could start using the barely existing tag stretchy.

a_good_time

monkey_d._luffy

a grower, not a shower

Let's see... Other boorus don't seem to have a tag for that. And TVTropes calls it rubber man.

Which would be a poor name for the tag, since they generally don't look like they're made of rubber.

...this one seems hard to name.

I'd say +1 to stretchy.