Rumble is a Legendary elemental-type fruit in Blox Fruits. It is expensive and hard to obtain Rumble fruit. It costs $2,100,000 or 2100 Robux and has a 2.25% chance of being in stock, so it will take some time to show up in a shop. It has a spawning chance of 2.30%, so there is a low chance that you will find it while playing.
Rumble is more PVE than PVP type of fruit. With Rumble, you will be able to stun targets for a long time, have great mobility, and be able to do AOE damage. Now the problem with Rumble is that it does not have a lot of high-damage skills, which is extremely bad for PVP. The best place to use this fruit is to farm bosses. Overall, decent fruit, but there are much better fruits that you can get, so if you do not like it, trade it away.
What combo you will use depends on your in-game situation, who you are fighting with, and what you want to achieve. It is best to spend some time testing all possible combos, and by doing that, you will learn how to use what works best for you and also how to counter it. So go and test Rumble in a game.