There is no stable coin here in crypto their prices always based on the very first one Bitcoin. Even bitcoin don't do stable so all its alts are affected. Whale traders have the controls of market since the past few years maybe soon things would change when bitcoin is known all over the world all countries will use bitcoin I think it is the time all alts would had a stable market movement.
Of course there are stable coins in crypto, not all the coins are "pegged" to Bitcoin - Tether (USDT) is pegged to US dollar. And this week was launched True USD (TUSD), another coin which is pegged to dollar. Both of them are stable because their entire circulation supply is backed by the same amount of dollars.