Many moons ago informal
a long time ago
Even though I travelled to Vietnam many moons ago, until now I cannot forget the taste of 'Banh mi'.
Many moons ago, I used to be really shy when meeting new friends.
Jack just finds out that he was adopted many moons ago by his parents.
To remain influential in a particular situation or a particular group of people for a long time
Time is running out.
This expression means something will occur in the near future.
Blind man's holiday is the time between daylight and darkness when people cannot work because it is too dark to see.
To eagerly and decisively do something when you have the oppotunity to
'Many moons ago' describes the time in the past, therefore, the verb in the sentence should be in the simple past tense.
Based on Etymology, there is one Native American legend, the Winnebago Legend, which told that the good spirits and the evil spirits agreed that the calendar year should be divided into 12 moons, which corresponded to the number of stripes on one chipmunk's tail. The six white stripes represented the ‘winter moons’ while the remaining six black stripes were the ‘summer moons’. Therefore, 'moon' refers to 'month' and used as an ancient measure of time.
To be very wet
Because of forgetting bringing an umbrella, I look like a drowned rat when it rains.