Show canned hints
You want to start by solving the crossword clues. The answers share a commonality, which can help confirm them.
Each of the answers makes a two-word phrase with the word "index". As suggested by both this and the title, you definitely want to do indexing somehow.
Indexing the first three numbers (5, 3, 4) into their answers (REFRACTIVE, FINGER, FOSSIL) gives ANS. The fact that this is the beginning of the word "ANSWER" is relevant, though indexing into the other clue answers is not as simple.
It may be useful to think about why the clues are presented in a monospace font and are offset weirdly.
|giving it away||
Treat the letters in the clues as a word search.
When indexing with complex numbers, use the directions given by the complex plane (https://en.wikipedia.org/wiki/Complex_plane). It's easy to be off by one, so don't forget that, e.g. indexing 5 into REFRACTIVE should still give A.
As an example of indexing 1-8i into PRICE, you can start at the space above the "p" in "pay", then move down to the "p" in "p" for the 1, and then move 8 characters left to the "w" in "crowd" for the -8i. This gives the W in the word ANSWER.
The solution to this puzzle is the 6-letter word made by indexing the same way into the last 6 words.
Like an object that curves or bends light (5) With “the”, a derisive sign also frequently called the bird (3) Buried remains of a Dracorex or a Brachiosaurus, e.g. (4) This determines the sum paid in a purchase (1-8i) A king, ace, or jack is an example of this component of a deck (20) With “crowd”, to pay for a specific project as a large group (0) Relating to blood glucose levels (5-4i) A finger that might be green or opposable (4i) What an exothermic reaction produces as a side effect (-4) Item traded on exchanges such as Euronext or Nasdaq (8) A basic data structure that can be dynamic or associative (-2) It may be genitive, objective, dative, or ablative (3.5+0.5i)