In the 2nd phase of the fight you normally have to wait for Ook to bring you bomblings to use on diababa however you can use bomb-arrows or juggle bomblings from the 1st phase to avoid having to wait. Doing it without bomb-arrows requires certain positions and being able to target fast. This trick saves around 30 seconds.
Firstly you should know that when a bombling is inside your boomerang the timer resets, this is used to keep the bomblings for the 2nd phase.
1) During phase 1 kill the first diababa head on the left normally
2) Stand on the edge near the water in the middle and boomerang the 2 left most bomblings to you (the position matters so the bomblings are infront of you at the start of phase 2
3) One of the bomblings will be in your hands, keep targetting until you target the bombling to the right then use the boomerang to drop it next to the other one. You then also use this bombling on the right to finish phase 1
1) During the CS you want to mash boomerang and hold target to instantly throw the boomerang at diababa and also pick up bomb bomblings from phase 1 in the boomerang. If the bomblings are not in the boomerang then the positioning of dropping them in phase 1 was wrong
2) You also want to be holding down during the CS so you instantly start backing away from diababa, once you have moved down slightly you want to go down left to the point shown in the video which can be described as the left of the 3rd plank from Diababa on the floor
3) As soon as you can throw the bombling in you hand towards Diababa (Still targetting). The other will drop to your left for you
4) Quickly back against the wall and target the bombling nearest and then Diababa, this should make the first bomb hit Diababa (because it is high in the boomerang) while also picking up the further bombling which should be lower in the boomerang and therefore not hitting him
NOTE: If both bomblings blow up on Diababa then the 2nd bombling wasn't low enough, to counter this try going further left when backing for the first time
5) After your thrown the boomerang wait a little so you don't walk into the boomerang and pick up the bombling, then walk to the middle of the 3rd plank (the same plank you collected them both on) and look to your right away from Diababa. As a visual que you can line up your 3rd heart roughly with the left of the waterfall
6) When the bombling that didn't hit Diababa comes back wait a split second so Diababa can fall some more then throw the boomerang to the right which will send you 2nd bombling away to safety while you deal the first cycle of damage. To deal the damage you should target him while he is falling and stand on the left of the 3rd plank, this way you can jump attack into a spin attack
7) The bombling should come back just after you finish cycle 1, you can now look up at Diababa and throw the boomerang with the bombling again to hit him back down
8) Finish him off. Again the fastest is jump-attack into quickspin although not needed this time