What literary element is "Shakespeare is hard"? What literary element does this sentence have an example of: "On the pallid bust of Pallas,...

I'll add the following to your
answer. 

Pallid and Pallas do create alliteration with the
"p" sound, and they also provide repetition and unity with the use of assonance:  the
repetition of vowel sounds (short "a" sounds, in this case).  They do not constitute
internal rhyme, because they do not rhyme:  the final syllables are not identical and do
not sound the same.  Variations of true rhyme do exist, but -id and -as in the final
syllables do not fit into any category of
rhyme.

"Shakespeare is hard," I believe, is an example of
synecdoche:  naming a whole for its part.  "Shakespeare" means "reading Shakespeare." 
Shakespeare, the person, is not literally hard.  Reading him can be.  I'm not entirely
sure about this, but the figurative language being used seems to involve naming. 
Another editor may be more certain.

Finally, I believe
"wind with a wolf's head" is simply metaphor.  The wind is being compared to the head of
a wolf.  The wind is the tenor of the metaphor (what the writer wants to describe), and
the wolf's head is the vehicle (what the writer uses to describe the tenor).  There is
an obvious comparison, and neither like or as is used, which would make it a simile. 
Instead, the comparison is direct, which makes the line a
metaphor.