Wim Hof

Hof holds records for prolonged ice immersion and climbed part of Everest in shorts, and unlike most people making such claims he has submitted to laboratory study: published research at Radboud University found that he and trainees using his breathing method could influence their immune response to an injected toxin, which had been assumed impossible. The method is also sold commercially, through courses and an app, and the breathing exercises have killed people who did them in water, because the technique can cause blackout with no warning. His own instructions say never to practise in or near water, and the deaths happened anyway.