How do you unlock tarble in db raging blast 2?

You can't unlock Tarble in Dragon Ball Raging Blast 2. He is not a playable character in that game.

The playable characters in Dragon Ball Raging Blast 2 are:

* Goku

* Vegeta

* Gohan

* Trunks

* Piccolo

* Gotenks

* Future Trunks

* Bardock

* Broly

* Cell

* Freeza

* Majin Buu

* Kid Buu

* Super Saiyan 4 Goku

* Super Saiyan 4 Vegeta

* Super Saiyan 3 Goku

* Super Saiyan 3 Gotenks

You might be thinking of another Dragon Ball game where Tarble is playable, such as Dragon Ball Xenoverse 2.