Where to start! Well, finding some rare arable plants, like Prickly Poppy or Corn Cleavers, would be excellent. Rootless Duckweed would also be nice, if only to see a British example of a world record holder without having to watch the Olympics! On the zoological side, I'd love to see any British species of jellyfish, but especially a large one like a Lion's Mane or Barrel. Finding odd arthropods like Euscorpius, stick insects, or mole crickets would be fascinating, as would spotting a Common Octopus. Any snake is likely to drive me into a frenzy as well. Finally, Tufted Puffin is the most unlikely species to turn up on these shores again, but it is one of my favourite bird species so I'm holding out for another sighting.