people, first of all, to get [no encounters] ability you only need about 20 minutes, not 2 hours, and why the heck would you go to omega ruins to get it???
ok, here we go, to get [purifying salt x 99] just capture the following monsters and you will get them from the monster catcher:

1 Vouivre [Mi'hen Highroad] x4
2 Lamashtu [Mushroom Rock Road] x4
3 Kusariqqu [Thunder Plains] x4
4 Mushussu [Sanubia Desert] x4
5 Nidhogg [Cavern of the Stolen Fayth] x4

now, to get the celestial mirror, first win the race at reminem temple, then go to macalania woods and speak with the mother and child, then go to campsite and talk to the father(he runs off) go back and keep talking to the mother until she says that the kid is missing, then go to that sparkly path and speak with the boy. touch the plant and you will have celestial mirror. this is the place where you use the sigils and crests to unlock your weapons!