Expressions: extremely determined to do something, even if it is wrong

go to any lengths:
to be willing to do anything, even if it is cruel, dishonest, or illegal, in order to get what you want
Example: He's prepared to go to any lengths to find the men who killed his daughter.

be hellbent on:
informal to be extremely determined to do something, especially something dangerous or something that may have a bad result.
Example: Bob's hellbent on going through with the plan, even though it's sure to end in disaster.

come hell or high water:
use this to emphasize that you are determined to do something in spite of any problems or difficulties.
Example: I'll be there in time. Don't worry. Come hell or high water.

Expressions: To suddenly forget something

it's on the tip of my tongue
Use this to say that you know a name or word, but you are having difficulty remembering it at that moment.

dry up
To forget what you were going to say or what you are supposed to say when speaking or acting, especially because you are nervous.

your mind goes blank
If your mind goes blank you are suddenly unable to remember something at a time when you need it.