Like any other boss in Beyond, he also awards the user 50,000 Ryo.
Garaa stands on the front of the sand dunes near Sunagakure, if he is attacked he will relentlessly assault you. He has a habit of using Sand Jutsus throughout the fight.
The best strategy for Gaara is to spam melee while you keep spawning a clone whenever you estimate your previous clone is about to disappear. The clone keeps Gaara's attacks focused elsewhere, and spamming melee is the best way to damage Gaara quite a bit and prevent him from using jutsu. When fighting Gaara, unless you are C Rank+, do NOT use any kind of knockback jutsu/modes. It is advises to not use any jutsu whatsoever, but definitely not knockback jutsu/modes. Knocking Gaara out of your clone's range can cause him to glitch out and disappear, or give him a chance to use a jutsu.
Note: Don't let him near any one the sand dunes. They have extremely glitchy meshes and can easily cause Gaara to glitch out completely.