When you need to delete a bunch of cards in one swoop. I use this in Google script.

gistfile1.gs

TRELLO_API_KEY = 'trelloUserToken';
TRELLO_API_TOKEN = 'trelloAppToken';
LIST_ID_TO_DELETE = 'trelloListId';

function trelloRequest(url, options) {
  var authUrl = url + '?key=' + TRELLO_API_KEY + '&token=' + TRELLO_API_TOKEN;
  
  var response = UrlFetchApp.fetch(authUrl, options);
  var responseText = response.getContentText();

  return responseText;
}

function deleteCard(cardId) {
  var url = 'https://api.trello.com/1/cards/' + cardId;
  var options = {"method" : "delete" };
  
  return trelloRequest(url, options);
}

function getCards(listId) {
  var url = 'https://api.trello.com/1/lists/' + listId + '/cards';
  var options = {"method" : "get" };
  
  return trelloRequest(url, options);
}

function formatCardIds(cardsResponse) {
  cardJson = JSON.parse(cardsResponse);
  var cardIds = [];

  for (var i in cardJson) {
    var card = cardJson[i];
    cardIds.push(card.id);
  }

  return cardIds;
}

function fknDeleteTheCards() {
  var cards = getCards(LIST_ID_TO_DELETE);
  var cardIds = formatCardIds(cards);
  for (var j in cardIds) {
    var cardId = cardIds[j];
    Logger.log('Deleting card - ' + cardId);
    deleteCard(cardId);
  }
}