Say I have two Profrssor’s Letters which allow me to search for two basic energy cards then shuffle my deck afterwards. In competitive play, are you able to play two of those cards or similar cards at once to look for four basic energy at once.
You play Professor's Letter, search for two Energy cards in your deck.
Then you show the second Professor's Letter to your opponent, and search for two more Energy cards, without shuffling between the two.
Taking time to shuffle between the two maybe considered slow playing in tourneys, even if technically legal.