Haribol Prabhu,
Sorry for the late reply. According to The Glories of Ekadasi translated by Bhumipati Dasa. The fast is a standard fast for Mohini Ekadasi. The benefit derived is that you can be purified from all sinful reactions. It's not that we should have any intention or desire in mind however. The book I've mentioned is a wonderful book that shares past times of the Lord and the various ekadasis.
Pertaining To Lord Narsimhadev's appearance day. The fast is until dusk (no food).
I hope this was helpful.
Dhama-Rupini
Yes Nrsimhadeva's appearance day is a simple fast till dusk, the period between daytime and nighttime. No food, one can however take water if one wishes.
Mohini Ekadasi is a standard ekadasi, the only one that is different is Pandava Nirjana Ekadasi, Hare KRishna
ys
ncd
