*starts collecting his Katon chakra in his stomach*
When he thinks that he has enough if it, he stops. He starts moving it towards his gullet and further. Whene the chakra gets really close to his mouth, he jumps as high in the air as he can, turning toward the sensei's clone. When he gets to the highest point, his chakra arrives to the end of his lips and he uses shape manipulation and starts making the special fire bullet. Already when the bullet isn't fully formed, he makes it to have the ability to erupt into a geyser. When the bullet is ready, he shoots it towards the opponent, but he misses because he wanted to. He severely makes two more of the fire bullets with same characteristics and shots it towards the clone. He misses again. He sees the little smile on the clone's face, but when he starts falling, near to the ground, he claps with his hands and triggers the bullets and three massive geyser of flame appears. They easily destroy the clone because they spread almost all over the field. He controls them not to hit him, though.
I think that the disadvantage of this technique is that the user needs to jump in the air for it to function normally. And if the opponent is skilled enough, he/she is able to interrupt the user. The advantage of this technique is that it's a double threat. If you miss with the first shot, you can make the geyser which is the real use of this technique. Pretty unpredictable, too.
*performs a sequence of 4 hand seals*
He takes a deep breath and while inhaling, he starts gathering his Katon chakra in his lungs. When he thinks that the chakra is ready, he starts exhaling and whilst doing that, he starts moving the chakra towards his mouth, When the chakra get to the end oh his mouth, he uses shape manipulation ans starts making a gust of ash. But, this is a special ash. He spreads more pieces of it's chakra through it and heats it up to be very hot in it. When he sees that the ash has covered the sensei's clone, he triggers all of the pieces of his chakra by clicking with his teeth. When he does that, a massive explosion ensues and starts burning the hell out of the clone. The clones disappears in a split of a second because the burns were very serious.
The advantage of this technique is that it's very unpredictable. The opponent thinks that there's only ash that suposses to blind them but when they see the explosion, it's far too late. The disadvantage of this technique is that the user must be really careful when using it because he/she needs to read the air currents, the insight to read the movements of the enemy, the tactical experience to not also enfold one's allies in the flames, and careful attention for the timing of the ignition.