The Sentence Diagram Generator is designed to visually represent the grammatical structure of the provided sentence. Here is the diagram for the sentence:

[While] [narwhals] [had been seen] [before] [using] [their tusks] [to stun] [fish] [before] [eating] [them], 
[they] [now] [have been stabbing] [and] [slashing] [the fish] [with] [both] [the tip] [and] [shaft] [of] [their tusks], 
[disabling] [and] [possibly] [killing] [the fish] [before] [consuming] [their prey].

This representation breaks down the sentence into its main components, illustrating the relationships between subjects, verbs, and objects, as well as the various clauses and phrases.