nicer
nicer
nicer, nicest
No. The word nicer is a comparative form of the adjective nice. The adverb is nicely and the comparative would be "more nicely." (*The term "play nice" is just a colloquial form; play nicely is correct.)
The comparitive form of the word nice is nicer, but whatever you do, don't just add 'er' onto the end of every word to make it comparitive!
nicer
Nicer
"Litter" is a noun and a verb and, as such, does not have a comparative degree.
nicest, nicer
smoother is comparative of word smooth.
A comparative for the word ineffectual is more ineffectual.
more nicely
The comparative is hotter.