Both Uses of

mock

in

Twelfth Night

Get ye all three into the box-tree: Malvolio's coming down this walk; he has been yonder i' the sun practising behaviour to his own shadow this half hour: observe him, for the love of mockery; for I know this letter will make a contemplative idiot of him.†
Scene 2.5 *

mockery = something that is ridiculous OR the teasing of someone in a disrespectful manner

I have said too much unto a heart of stone, And laid mine honour too unchary on it: There's something in me that reproves my fault; But such a headstrong potent fault it is That it but mocks reproof.†
Scene 3.4

mocks = makes fun of

Definitions:

(1) (mock as in: don't mock me)
make fun of (ridicule--sometimes by imitating in an exaggerated manner)

or (more rarely): just to make fun or to be ridiculous without targeting anyone as a victim

These senses of mockery come together when a comedian pokes fun at a politician by pretending to be the politician and saying ridiculous things.
(2) (mock as in: a mock trial)
not real
(3) (meaning too rare to warrant focus)
Less commonly, mock can refer to a way of preparing food. Mockers can be an abbreviation for mockingbirds.