Certain forms of poetry constitute a challenge all their own. The sestina, which has an elaborate rhyme scheme that retains the same six end-rhymes but rotates them from stanza to stanza. The villanelle must be one of the most difficult such forms. One of the most famous of these is Dylan Thomas's "Do Not Go Gentle." The scheme of the villanelle isn't to keep simply an end-rhyme, but to retain one full line of the original triolet in each subsequent stanza and then in the final stanza to repeat all three lines with one additional line.
Here's an example from Edwin Arlington Robinson which is quite pleasing.
Villanelle of Change Edwin Arlington Robinson Since Persia fell at Marathon, The yellow years have gathered fast: Long centuries have come and gone.And yet (they say) the place will don
A phantom fury of the past,
Since Persia fell at Marathon;And as of old, when Helicon
Trembled and swayed with rapture vast
(Long centuries have come and gone),This ancient plain, when night comes on,
Shakes to a ghostly battle-blast,
Since Persia fell at Marathon.But into soundless Acheron
The glory of Greek shame was cast:
Long centuries have come and gone,The suns of Hellas have all shone,
The first has fallen to the last:—
Since Persia fell at Marathon,
Long centuries have come and gone.
