Hard Rock World Tour Charm parties are the best deal in the game for Charms/Coins. Players who don't take advantage of the party system are missing out, so we strongly advise all players to use their Party Passes. We understand not everyone wants to attend the parties, but we'll never stop awarding them as the players who do use them don't want to miss out.
Party Passes pool all their values into the Party Credits. For example, if someone gives you Party Passes worth 1,000 Gems, you now have the option of using the value of that pass to go to any party you want to. That could be a single Mushroom party (using 850 of your Credits) or it could be an assortment of lower cost Parties.
If you have some Party Pass Credits, the total is displayed at the top of the Parties Screen in the upper right corner. If you are currently in a game, click on Hard Rock World Tour in the upper left corner of the screen, and the Parties tab will appear at the top of the screen.
When paying for Charm Parties, Hard Rock World Tour will always use your Party Pass Credits first, before any Gems. If you don't have enough Party Pass Credits to pay for a Charm Party, the game will automatically deduct the remaining balance from your Gem total (So if you have 14 passes and go to a 20 Gem party, it'll cost a total of 14 passes and 6 Gems.)