There is no plural form for the noun dismay. Dismay is a state of being, you are either in that state or you are not. When you need to say that a number of people are in the state of dismay, you use the adjective form, the dismayed people, or the verb form, they were dismayed.
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "was" is "were."
The plural form of "I" is "we."
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.
The plural form of the demonstrative pronoun 'that' is those.
Trenches is the plural form.
The plural form is metres.