Alchemy.Client.delete_messages

You're seeing just the function delete_messages, go back to Alchemy.Client module for more information.
Link to this function

delete_messages(channel_id, messages)

Specs

delete_messages(snowflake(), [Alchemy.Message.t() | snowflake()]) ::
  {:ok, nil} | {:error, term()}

Deletes a list of messages.

Requires the MANAGE_MESSAGES permission for messages not posted by this user. Can only delete messages up to 2 weeks old.

 Cogs.def countdown do
   {:ok, m1} = Cogs.say "3..."
   Process.sleep(1000)
   {:ok, m2} = Cogs.say "2..."
   Process.sleep(1000)
   {:ok, m3} = Cogs.say "1..."
   Process.sleep(1000)
   Client.delete_messages(message.channel, [m1, m2, m3])
 end