Find a ship and Return crystals to mystic are missions in Going Commando taking place in the mining area, Tabora. After Ratchet and Clank escaped the underground tunnels, the two searched for a ship to leave the planet. To their surprise, they found their crushed ship, the Star Explorer, in the middle of a town in the mining area, in the possession of the Mystic, a mysterious guru who told them that possession was "an illusion". He offered to repair the ship in exchange for ten desert crystals. Having no better ideas, the two searched the desert for them.
The mission begins as soon as you enter the town, and a cutscene will commence. After this, you are required to obtain ten desert crystals. Tabora's desert dunes contain one hundred crystals in total, many of which are obtained by smashing a purple shell in which they are contained, while others are obtained by beating a species of large desert dune monsters. The Pulse Rifle is extremely useful against the monsters, while the Synthenoids, Seeker Gun, Miniturret Glove and Lava Gun are useful against the rest of the enemies.
To obtain the ten you need now, the easiest way to do this is by heading across the bridge on the left of the town to a portion of the dunes surrounded by a canyon. Smash the purple shells containing crystals to obtain them, and kill desert dune monsters. Desert dune monsters are best killed with the Pulse Rifle. When approaching their debris hiding spot, a dune monster will pop out, and shoot a laser from its eye that sweeps the floor; simply aim the Pulse Rifle and fire three times to kill it before it can even get a hit. Make sure you have the Synthenoids active at all times; if you run out, return to the vendor to restock. Collect all twelve crystals here before you leave, and return to the Mystic. Giving him ten crystals will complete the mission, and all remaining crystals can be sold for 1,000 each.
Before leaving to Dobbo, consider obtaining more desert crystals. However, you do not have to obtain them all right away; consider obtaining twenty for now (thirty total after the ten for the first mission). It is wise to return to Tabora after completing the missions in Joba later, as the Charge Boots will make it significantly easier, while the Gravity Boots allow you to make use of a mining vehicle and mine for Raritanium for your ship. Also, if you have not already, complete "Explore the area" first.
When done, travel to Dobbo for the next mission, "Explore the testing facility".