Omanyte's role is self-explanatory (spikes are hella good when your team doesn't have many immediate ways of doing damage), drowzee checks a vast majority of the tier's special attackers, chips things with seismic toss (which is borderline insane when everything has around 200-300 max hp) and passes wishes to its least self-sufficient teammates, shuckle works as a pivot against stuff like dragonair and helps pp stalling some slow set up sweepers like curse/swords dance ivysaur who'd otherwise single handily run through my 6, tentacool looks like a weird choice aside from rapid spin but it serves a very specific purpose as one of the tier's most reliable answers to clamperl, which is going to be doing around 30% max with hidden power, mightyena provides heal bell support and phasing and bayleef is the team's primary ground-type switch in. it can be really annoying to play around with spikes up and constantly threatening to leech seed the opponent's threats but it still works nonetheless.