In antithesis, the same sentence contains a striking opposition or contrast of words or sentiments. Antithesis is employed to secure emphasis.

Man proposes, God disposes.
Not that I loved Caesar less, but that I loved Rome more.
Give every man thy ear, but few thy voice.
Speech is silver, but silence is Golden.
Many are called, few are chosen.

Oxymoron

Oxymoron is a special form of antithesis. It conjoins two terms that in ordinary usage are contraries.
She accepted it as the kind cruelty of the surgeon’s knife.
So innocent arch, so cunningly simple.

Phrases like ‘pleasing pains’, ‘I burn and freeze’ and ‘loving hate’ are all examples of oxymoron.

Climax

In climax, a series of ideas are arranged in the order of increasing importance.
Simple, erect, severe, austere, sublime
What a piece of work is man! How noble in reason, how infinite in faculties! In action, how like an angel! In apprehension, how like a God!

Anticlimax

Anticlimax is the opposite of climax – a sudden descent from higher to lower. It is chiefly used for the purpose of satire or ridicule.

Here thou, great Anna! Whom three realms obey,
Dost sometimes counsel take – and sometimes tea.