The Gold Capsule is a petling capsule in RoPets that can only be acquired through official giveaways, from select influencers that are included in the RoPets Influencer Squad, or from @SuperBevarooni on Twitter. This capsule's availability is limited as there is no way to purchase it directly in-game.
There is a better chance of hatching a petling with a higher rarity from a Gold Capsule. Gold Capsules do not hatch into common or uncommon petlings.