Use up a specific leftover

Half a tub of something staring at you and three days left on it.

I have a leftover to use up. Give me real options, not a list of things it could theoretically go in.

Give me four uses, ranked by how completely they use it up:
1. One that uses all of it as the main event
2. One that hides it in something else
3. One that needs only store cupboard items alongside it
4. One that preserves or transforms it so it keeps another week, for example freezing in a useful form, turning it into a sauce, or pickling it

For each: what to make, the extra ingredients needed, and the time.

Then tell me first whether this is still safe and good to eat given how it has been stored and for how long. If it should be thrown away, say so straight away and do not suggest recipes for it.

Leftover and rough quantity:
How long it has been in the fridge and how it was stored:
What else I have:

Cooking from what you have. Dinner out of the fridge as it stands, leftovers to use up, and swaps for the thing you are missing.