Mustard
No, you did not read that wrong. Mustard can be used as a remedy to remove mustard stains but it is not a foolproof method. If you know what the exact type of mustard on your clothes is, then you can cover the stain with the same type, let it sit for a couple of minutes and then wash it off. This method may work because the ingredients in the fresh mustard may revive the old stain, which will make it easier to remove. But as mentioned earlier, this is not a completely safe method.