You may exert Watchful Naga as it attacks. When you do, draw a card. (An exerted creature won't untap during your next untap step.)
Related products

from $5.34
Bontu's Monument
Amonkhet
Black creature spells you cast cost {1} less to cast. Whenever you cast a creature spell, each opponent loses 1 life and you gain 1 life.

from $2.66
Harvest Season
Amonkhet
Search your library for up to X basic land cards, where X is the number of tapped creatures you control, and put those cards onto the battlefield t...
View full details
from $0.49
Wayward Servant
Amonkhet
Whenever another Zombie enters the battlefield under your control, each opponent loses 1 life and you gain 1 life.

from $1.48
Lord of the Accursed
Amonkhet
Other Zombies you control get +1/+1. {1}{B}, {T}: All Zombies gain menace until end of turn.