This is an entry into the Fortnightly Topic Challenge #36. [edit: i hope this wasn't too bad for my first puzzle here! let me know how i did :)]
The answer to this puzzle should answer the question: what is required to solve this puzzle?
Across
1. Many hands make this? (7, 2 wds.)
3. Promotion (2, abbr.)
5. Transformation's namesake (4)
7. Expression of disgust (4)
8. Frequently (3)
10. Nickname for mother (2)
11. European currency (4)
13. Resembling a lion or a certain pope (4)
15. Brand name of Furosemide (3)
17. Injury caused by repetitive mechanical exertions (3, init.)
18. Canvas (2)
19. Takes revenge (4, 2 wds.)
Down
1. To produce an egg (3)
2. Sharp increase in price (4)
4. Comprising two parts (4)
5. Forked or branching (4)
6. Abnormal narrowing of a passage in the body (6)
9. Transport goods in bulk (3)
10. Of metal, in liquid form (4)
12. Reactive (4)
14. Spanish form of "bravo" (3)
16. Name of sign found in email addresses (2)


