Krishna fighting with Agni and Varuna is described in Vishnu Parva of Harivamsa. These events happened at the time of Aniruddha marriage.
Fighting with Agni happened just when entering in the Shonitpur, the city of Banasur. It is described in Harivamsa, Vishnu Parva, Chapter - 122 as follows:
Then (bala)rAma spoke these words to kR^iShNa who is incomparable in battle:
(balarAma said:) O kR^iShNa! We have lost our splendor. How did this happen which
never occurred before?
All of us are covered by a golden colour. There is no doubt. Tell us the reason
why this is so? Are we going by the side of the meru mountain?
The auspicious lord (kR^iShNa) said:
O the oppressor of foes (balarAma)! Understand that the city of bANa is certainly
near. The fire has come out (of the city) blazing for protecting the city.
We are opposed all over by the splendor of the fire AhavanIya. O the one who has
the plough as weapon (balarAma)! That is why the change of colour has occurred
to us.
The auspicious (bala)rAma said:
If we are near the city and if we have lost our splendor, then think with your
intellect and do the next according to your wish.
The auspicious lord (kR^iShNa) said:
O the son of vinatA (garuDa)! Do what is to be done here next. After you do what
is to be done according to you, I shall do the best what is to be done.
vaishampAyana said:
(O janamejaya!) Hearing what was told by the son of vasudeva (kR^iShNa), the
powerful garuDa who can take up any form as he desires, created thousands of faces.
Afterwards, the highly powerful son of vinatA (garuDa) went to the river ga~NgA.
Jumping into the divine river AkAshaga~Nga, he drank lots of water.
The splendorous son of vinata (garuDa) showered water standing above. The son of
vinata (garuDa), the one having intellect, extinguished the fire with water.
The fire AhavanIya was thus pacified.
After Ahavaniya defeated some other fires also fought. This is described as:
As the fire was subdued, the king of birds, garuDa proceeded further, making
terrible and loud sounds by waving his wings powerfully.
Seeing them there, the followers of rudra (shiva), the fires wondered: Who are
these men having different terrible forms, mounted on garuDa?
What purpose did they come here? Who are these three? Those fires of the mountain
could not reach any decision.
Then the fires fought the battle with the three yAdava-s. While they were engaged
in the battle, loud sounds were heard.
Hearing those loud sounds, similar to the roaring of lions, a~Ngiras, the one
with intellect, sent his man (to find out).
(a~Ngiras said:) Go to the place where the battle is going on. Do not delay. See
everything (the battle) and come back. Saying this, the man was sent quickly.
Saying let it be, the person went to see the battle between the son of vasudeva
(kR^iShNa) and the fires in the great battle field.
All those fires, kalmASha, kusuma, dahana, shoShNa as also the highly powerful
tapana,
those five fires are famous in the consecration by uttering svahA (while offering
oblation to fire ).
There are other highly splendorous fires along with their armies, named piThara,
pataga, svarNa, shvA, gAdha as well as bhrAja.
These five fires based on svadhA were also fighting there.
Two fires, great souls with the great splendor of jyotiShToma division and based
on vaShaTkAra also fought there, mounted on the chariot of fire and holding
sparkling arrows.
Among them the great sage a~Ngiras dazzled in the battle.
Seeing sage a~Ngiras releasing sharp arrows in the battle, kR^iShNa became angry.
Smiling again and again, he said:
All of you fires! Halt! I shall create fear for you. Burning in the splendor of
my arrows, you will run far away in all directions.
Then sage a~Ngiras came running with a sparkling trident, becoming angry to take
away the life of kR^iShNa in the great battle.
kR^iShNa cut the sparkling trident with his crescent shaped sharp arrows similar
to those of the god of death.
Then the great soul kR^iShNa split the chest of sage a~Ngiras with sparkling
arrows named sthUNakarNa, equal to those of the god of death.
a~Ngiras was distressed with blood flowing from his body. He suddenly fell down
on earth with his stunned body.
All the remaining fires, the four sons of brahmA ran away quickly to the city of
bANa.
And the fighting between Krishna and Varuna happened just after the marriage of Aniruddha as described in Harivamsa, Vishnu Parva, Chapter - 127:
Travelling through the sky, they reached the place of varuNa. The great souls
saw thousands of the cows yielding divine milk, having many colours, moving in the
forest near the ocean.
Knowing about the cows, depending on the words of kumbhANDa, kR^iShNa, the best
among strikers and also the expert who knows the truth,
ecognizing them as the cows of bANa, decided to have them. The one who is foremost
in the world, the one who does not have any decline, kR^iShNa, seated on garuDa,
said:
The auspicious lord kR^iShNa said:
O the son of vinatA (garuDa)! Proceed to the place where the wealth of cows of
bANa is. It is said that immortality is achieved by drinking their milk.
satyabhAma told me: Bring the cows of bANa for me. By drinking their milk, the
great demons do not become old.
Living beings (it is said), discarding decay, will become unaffected by old age
(by drinking their milk). If right conduct is not compromised, bring the cows.
Let there be good to you.
Otherwise, if any compromise is to be done in your work, do not keep your mind on
this. Thus satyA (satyabhAmA) told me. I have recognized the cows.
garuDa said:
These cows see me. Seeing me, all of them begin to enter the residence of varuNa
immediately. Do what is to be done here.
(vaishampAyana continued: O janamejaya!) Saying this, garuDa agitating the ocean by
generating winds by fanning his wings, entered the residence of varuNa.
Seeing that garuDa has entered the residence of varuNa, all the beings of the ocean
became confused and started moving.
Then the army of varuNa, most difficult to conquer, knowing this, arrived there,
taking various weapons, in front of the son of vasudeva (kR^iShNa).
Then there was a terrible battle between the beings of the ocean and the enemy of
serpents (garuDa).
After Garuda has defeated the being of ocean, Varuna himself appeared with his army.
The lord of water, highly furious, along with his sons, grandsons and army, shook
his great bow, as though he was challenging for battle.
lord varuNa, arrived there immediately, blowing his conch. The angry lord, varuNa
shot a group of arrows at hari (kR^iShNa) as if he was hara (shiva).
Then the one who agitates people, kR^iShNa, blew his conch pA~nchajanyaM,
born from water (obtained from ocean). The highly powerful kR^iShNa covered all
directions with groups of arrows.
Then varuNa was oppressed by a pure group of arrows in the battle. varuNa battled
with kR^iShNa smiling.
Invoking the terrible weapon vaiShNava in the battle, the son of vasudeva
(kR^iShNa)spoke as follows to the one with intellect (varuNa).
(kR^iShNa said) I have taken this highly terrible weapon, vaiShNava, the killer of
enemies, for killing you. Now you shall stop.
Aiming the vaiShNava arrow at lord varuNa, lord kR^iShNa readied himself. The
highly powerful varuNa took up the weapon vAruNa and roared.
Water jets emerged from the weapon of varuNa. The one who wins battles,
(kR^iShNa) prepared to shoot the vaiShNava weapon to control the same.
The water jets shot by varuNa began to boil. The vAruNa weapon was burned as the
vaiShNava weapon blazed again.
As the highly powerful vaiShNava arrow blazed, all of them ran away in all
directions.
After this Varuna praised Krishna and seek forgiveness.
