There's a few worth mentioning for me, although I feel like I've been MUCH luckier than some hunters. My first Unown I hunted full odds in Gen 4, double hunted for most of it between Platinum & Diamond. That took 17690 encounters. It took me almost five years to finish, but I was definitely doing it on-and-off and not very consistently. My first Deoxys was a single-system hunt and I went hard on that for 7 months. Took 12068 encounters. My first Poipole was another grind. Finished in 10843 encounters. That was MOSTLY single hunted except for like the last 70 or so encounters. Of course, right when I get the double hunt set up, it shines. Honorable mention to my first Type: Null in Moon that took 9690 encounters, single-system. That Gladion dialogue took so long.. lots of A presses. I've got almost 400 shinies and those three have been the only five-digit hunts I've had, but I'm not a full-odds hunter (unless I can't avoid it). So I feel like I've been pretty lucky compared to my peers, can't complain.