I really like Pendora, it's design is cool and it has some nice niches, you can exploit. At least you can't say it completely sucks. I can see three different sets that seem to have potential.
1) Spikes / Toxic Spikes
112 base speed and both Spikes and Toxic Spikes via egg moves and enough bulk and speed to set up at least two layers of entry hazards? Sounds really nice when you ask me. Unluckily his support move pool completely sucks. As said in the OP it doesn't learn Taunt and Rapid Spin. The only really other good move on a defensive set would be Toxic. It doesn't have reliable recovery and Sleep Talk isn't a TM even longer, but it wouldn't work because it's bulk isn't amazing, just good enough to set up two or three layers.
2) Swords Dance
Again, 112 base speed and meh 90 base attack are enough to a run a SD set, especially in the lower tiers. It gets decent coverage with good STAB Megahorn, EQ and Rock Slide / Poison Jab for the third slot. Pendora also has Swarm as an ability, so SubSalac may be a good set to use. But tbh SubSalac never worked for me.
3) Baton Pass
112 base speed, Swords Dance, Agility and Baton Pass? A fast Baton Passer is always useful. It lacks Taunt, but still quite decent.
Now, it's time to post some sets:
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Offensive Spikes
Pendora @ Leftovers
Nature: Jolly
Ability: Quick Feet
EVs 16 HP / 252 Atk / 240 Spe
~ Spikes
~ Toxic Spikes / Rock Slide / Poison Jab / Toxic
~ Megahorn
~ Earthquake
That's a decent Spiker for an offensive team. It keeps offensive momentum, removes TSpikes and still lays down entry hazards, especially many Pokémon that are offensive oriented loves Spikes and you don't want to run a completely defensive Pokémon on a sharply offensive team, do you?
240 Spe-EVs assure you that Pendora is able to outspeed all base 110 speed Pokémon without a boost / without a Scarf. The only Pokémon you can outrun with 252 Spe-EVs are the Fly and the Ele / Fly genies who will probably not used in the same tier as Pendora. Also you fail to speed tie with other Pendora and most notable (not) Purugly.
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Chesto Rest + hazards
Pendora @ Chesto Berry
Nature: Impish / Careful / Jolly
Ability: Quick Feet / Poison Point
EVs: Mixture between enoug bulk and enough speed.
~ Spikes
~ Toxic Spikes
~ Rest
~ Megahorn / Toxic
This set is a gimmick, but it combines Pendora's ability to lay down entry hazards and a one shot recovery, before it dies. This allow you to get a suicidal millipede that can actually stay for a while before it dies and that means you will get some Spikes up before it dies. Nothing special though.
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Swords Dance
Pendora @ Life Orb
Nature: Jolly
Ability: Quick Feet / Swarm
EVs: 252Atk / 4Def / 252 Spe
~ Swords Dance
~ Megahorn
~ Earthquake
~ Rock Slide / Poison Jab
Megahorn coming from even meh 90 base attack hurts a lot, especially when you look at Pendora's high 112 base speed. After a SD it will deal good damage and it looks like a good end game sweepr.
(PS: +2 Megahorn vs standard Milotic: 84.2% - 99.5%)
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SubSalac
Pendora @ Salac Berry
Nature: Jolly
Ability: Swarm
EVs: 12HP / 4Def / 252Atk / 240 Spe
~ Substitute
~ Megahorn
~ Earthquake
~ Swords Dance / Rock Slide / Poison Jab / Baton Pass
Self-explanatory. Isn't it?
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Baton Pass
Pendora @ Leftovers / Salac Berry / Other Berry
Nature: Jolly
Ability: Swarm / Quick Feet
EVs: 252HP/ 16Def /240Spe
~ Swords Dance
~ Agility
~ Baton Pass
~ Substitute / Megahorn
Self-explanatory. Isn't it? OK, I'm too lazy to describe the set. It's simple, it doesn't need further description.
Opinion:
I'm kinda excited. A decent, reliable Spikes for the lower tiers? Hell yeah! 112 base speed and still being able to run offensive sets and being able to pass fast boosts. It's stat spread makes it able to be used on offensive teams and it absorbs TSpikes, which are always annoying.
Still, there are quite some downsides. Pendora has a SR weakness, it is not exactly bulky, it has at best enough bulk to lay down 2-3 layers of entry hazards before dying and it will die fast. It's move pool is really lacking and it would really desire certain moves to be more effective. Most notably Taunt, a reliable recovery move and maybe a phazing move.
Despite this downsides Pendora is really an useful Pokémon, but I certainly doubt it's going to be OU (Skarmory, certain Pokémon can easily set up on Pendora, etc.), but I think it will be a really useful Pokémon in UU or in a lower tier (NU wants to have a not completely horrible Spiker). When you would introduce Pendora into GenIV's metagame without the other Pokémon, I'd guess that Pendora would be a top UU or even stuck in BL.
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