Had had

>whomst'd've

>walk the walk

>used to use

get used to had had used

Lived a knight once poor and simple
Pale of face with glance austere
Spare of speech but with a spirit
Proud, intolerant of fear

He had had a wondrous vision
Ne'er could feeble human art
Gauge its deep, mysterious meaning
It was graven on his heart

>have to have had had

That's not how you'd have had used.

As a non-native speaker these things really interest me. Isn't 'had had' a legitimate way to use the past tense? As in, expressing some "thing" that the person had (used to have) in some moment?

Slightly off topic is the use of With / In. Like if i were to say "His hands were covered in / with"... Which one is the correct term? Just a matter of taste?

And what about off of? Is there any other way to express this?

And while we're at it, what about to / for? "Speak for / to group"?

Thanks.

At least for the last one, "speak for/to group"

If you are speaking for a group, you are representing them, you are their representative voice.

If you are speaking to a group, you are telling them something.

For "off of", you mean, "Get off of me!" ?

You could just say "off"
"Get off me!"
"Get off him!"

For "with/in", I think its a matter of taste. "His hands were covered in slime", "His hands were covered with slime".

The first one, "in", sounds more casual, slightly more poetic I guess because his hands are not literally in anything.

The second, "with", sounds more literal and normal.