For clefable, I'd say that putting the second 252 in HP is a sound idea- you're already boosting your other defenses a bit, so why not make it even more durable? With any luck, you won't even need to use Lucky Chant! You could opt to put into Speed instead, though, for reasons I'll get to in a bit. Before that, however, it's important to keep in mind that the Glitch Field strips away the Fairy Type's right to exist, so clefable isn't immune to RAWRchomp's clever tricktm like one might expect. As such, breeding a clefable to have Misty Terrain as its fourth move seems like a fine idea, especially since the dragon isn't exactly built for being outside the Glitch World.
Scolipede probably wants its 252 to go to it's Sp. Def- while it wont be taking very many blows, it'll still have some attacks slip through its defenses and a large chunk of Terra's team is equipped to aim at its weak spot. The fourth attack slot should definitely go to Protect, though- this move can be grabbed on it in exchange for a Heart Scale, which I believe makes scolipede the only pokemon to get both Speed Boost and a blocking move by that point in the game. Use that a couple times to cheese some extra Speed buffs out for your clefable, and watch your pixie actually outpace things with a small amount of extra (Stored) power to work with to boot! The extra Speed also makes clefable mostly immune to the Field's bonus to Crit. Rate (while claiming said bonus for itself), which should make Lucky Chant a little less mandatory for you.
I'd recomend keeping a handful of other 'mons on hand as well, since no plan is truly foolproof and RNGesus is a fickle god. Of course, there's also the fact that there's also the dungeon's midboss you need to worry about, and it takes a lot of backtracking to change your team out between the two...