Krishn counts His Vibhooti in the 10th Chapter pf Geetaa, as what is He? Let us see in prose form what is He? This description begins with its Shlok No 21 --

1 - Among the 12 Aaditya, son of Aditi, I am Vishnu.
2 - Among all lights, I am Soorya (Sun).
3 - Among Marut Dev (Vaayu Devtaa). I am the Vaayu Dev, one whose name is 'Mareechi'.
4 - Among the stars I am Chandramaa (Moon).
5 - Among Ved I am Saam Ved.
6 - Among Devtaa I am Indra.
7 - Among all Indriya Senses) I am the Mind (man).
8 - Among living beings I am Consciousness (Chetanataa).
9 - Among the 11 Rudra I am Shankar.
10 - Among the Yaksh and Raakshas I am the god of treasure Kuber.
11 - Among the eight Vasu I am Agni.
12 - Among the mountains I am Sumeru Parbat.
13 - Among the all Purohit, know me the Purohit of all god Brihaspati.
14 - Among the army chiefs I am Skand (Kaarttikeya).
15 - Among the water bodies I am the ocean.
16 - Among Maharshi I am Bhrigu.
17 - Among Speech or Sound I am the Omkaar.
18 - Among all kinds of Yagya I am Jap Yagya.
19 - Among stable things I am Himaalaya Parvat.
20 - Among all trees I am the Peepal Tree.
21 - Among all Devarshi (god Sage) I am Naarad.
22 - Among Gandarv (musicians) I am Chitrarath.
23 - Among Siddha I am Kapil Muni.
24 - Among horses, I am horse who originated from nectar of Ocean name as Uchchaishravaa.
25 - Among the elephants I am the King of elephants Aairaavat.
26 - Among the human beings I am King.
27 - Among the weapons I am Vajra.
28 - Among the cows I am Kaamdhenu.
29 - Among the ones who bear child according to rule of Shaastra, I am its cause is Kaam Dev.
30  - Among snakes Ii am Vaasuki.
31 - Among Naag I am Shesh Naag.
32 - Among water beings I am the water god Varun.
33 - Among Pitri I am the one whose name is Aryamaa Pitri.
34 - Among rulers I am Yam Raaj.
35 - Among Daitya I am Prahlaad'.
36 - Among the number counters I am Time (Samaya).
37 - Among animals I am lion.
38 - Among bird I am Vishnu's vehicle Garud.
39 - Among the purifiers, I am air.
40 - Among knowledgeable of Shastra (weapons), I am Ram.
41 - Among fish I am crocodile.
42 - Among the rivers I am Gangaa.
43 - Among all knowledge I am the spiritual knowledge.
44 - Among Discussions, debate. I am the discussion done for Tattwa Gyaan
45 - Among letters I am the Akaar (dimensional / shape / size).
46 - Among Compound (समास), I am Dwandwa Samaas (two words opposite - day and night).
47 - I am the Avinaashee Kaal who have his face every side, Viraat Roop and bearer of everybody.
48 - I am destroyer of all - I am the death.
49 - I am the Creator of future creation.
51 - I am the words, speech, senses, memory, wisdom etc situated in every woman.
52- Among singable Shruti, I am the Brihat-Saam song which is sung for Indra.
53 - Among all Chhand I am Gaayatree Chhand
53 - Among Months I am Maargsheersh month
54 - Among all seasons. I am Vasant Ritu (spring season)
55 - Among the cheaters I am gamble.
56 - I am the influence of influential people.
57 - Among winner I am their winning
58 - I am brave of bravery, I am power of powerful.
59 - Among poets I am Shukraachaarya.
60 - Among Paandav. I am Arjun.
61 - I am Saatwik emotions of Saatwik devotee.
62 - I am Vaasudev of Vrishni Vansh.
63 - I am one who punishes who makes trouble and the one who want to win I am victory.
64 - Among hidden sentence I am silence.
65 - I am the main knowledge of knowledgeable people.
66 - I am the Creator of all creation.

(1) Among the 12 Aaditya, I am Vishnu.
Aditi is one of the 13 wives of Kashyap Jee. And Kashyap Jee is the grandson of Brahmaa Jee (son of Mareechi). The 12 Aaditya are the sons of Aditi. They are actually the meeting points of the Sun and the Moon. Indra is the eldest Aaditya Vishnu is the youngest one (the last Aaditya) All the Aaditya come in 12 months. Vishnu Aaditya comes in the month of Paush, when the months are started from Maagh. The first Aaditya is of the month of Maagh, known as Arun. Thus Vishnu is the last month before the start of Uttaraayan and Arun is the first Aaditya after the start of Uttaraayan.

(4) Why does Krishn say, "Among stars I am the Moon." The Moon is certainly not a star.
Krishn states, "Nakshatranam aham shashi". A common translation for Nakshatra is "star", which is fine in a general sense, but we should not take the technical scientific definition of "star" and think that Nakshatra refers to it. In the Collins Cobuild English Language Dictionary, "star" is defined as: "Any of the small points of light, including planets and meteors, that are seen in the sky at night."

This is the meaning that we should keep in mind when Krishn says, "Among stars I am the Moon." In the night sky, nothing is brighter and more effulgent than the Moon. Thus that aspect of supremacy represents Krishn.

In chapter 15 of the Geetaa Krishn says, "I am the Moon which nourishes all the vegetables". This seems to be opposite to scientific evidence.
The light of the Moon does have impact on vegetation, but this is not a science that has been researched sufficiently by western scientists. In Aayurved certain plants must be grown and picked by moonlight for them to be effective in curing disease. This can be tested scientifically. The modern Aayurvedik producers do not follow this method, and as a result their medicines are hardly 100th as effective as the medicines produced by the traditional method. The traditional method also requires certain Beej Mantra to be chanted into the medicine for several lakhs of counts, and finally there must be worship of Dhanvantari (the incarnation of Vishnu who established Aayur Ved). All of these procedures create a subtle effect on the medicine which can be visibly see by the effect and even by taste. It is unfortunate that hardly any Aayurvedik doctors follow these scriptural rules when producing medicine, and as a result the Aayurvedik science is almost lost.

There are some vegetables and plants which grow exponentially in the night.

(46) Among the compound words (समास), I am Dwandwa Samaas
Samaas is the use of two or three words together. Samaas are four types. Dwandwa Samaas is one of them. In this Samaas two such words are used which are of equal status. In nature they might be opposite to each other but in status they are equal. Why did Krishn say that he was the Dwandwa Samaas among all Samaas? He wants to tell Arjun that He is not one, He is two. How? He has created this world in two opposite things, or ideas - such as day and night, pleasure and sorrow, hot and cold, light and dark, fire and water, white and black, mother and father. love and hate etc etc. That is why He said that He was Dwandwa Samaas among all Samaas. In all those pairs, both terms are opposite to each other but still both have equal status and both are necessary to understand the importance of each other.