Originally Posted by Fat Lucchini
It is a good question which endgame Pokemon deserve a spot in Mid (no higher I'd argue) because of the availability issues. I'd argue that Lapras, Starmie, Gliscor and Sawk are good for Mid. Not so sure about Clefable - no good STAB, slow, needs several turns to set up. Your risk of your set-up ending in a stray crit is very high. Whereas Gliscor and Sawk do not require much set up at all, and Starmie/Lapras help out with dragons and the 8th gym.
Clefairy comes at the nice level of 50, meaning that you almost do not have to train it at all if you so desire. Return comes free on Clefairy and if you want you can tutor Body Slam. Clefairy is not solely going to be setting up; it can dish out damage without having all 6 Cosmic Powers under its belt. Using vitamins will help increase the power of Return (if you choose to use it). Hell, if you're playing Black 2, you can even attach a Toxic Orb, which will let you get a free 140 BP attack, which is roughly equivalent to a 100 base Attack Pokemon using Return and comes with status immunity to boot. Clefable may be slow, but that doesn't mean it can't damage things sufficiently to be good.