I told myself I wasn't gong to explain this any more times, but I guess if I can at least catch two people at once...
OK - there are
two things required for a monster to drop a particular unique.
It has to be able to drop the right item type,
and it has to be high enough level for the unique version.
The item types a monster can drop depends on its TC (you hear this mentioned all the time). Pindle does indeed drop from a higher TC than Meph. Which means any item
type Meph can drop, Pindle can drop too. Pindle can drop Spiderweb Sashes and Phase Blades, just like Meph can. He can also drop Hydra Bows and Sacred Armours, whereas Meph cannot.
Each unique has its own level also. These are less well known. Windforce is only level 80, meaning that if a monster can drop Hydra Bows, it only has to be mlvl 80 or more to drop a Windforce. But Arachnids and Azurewrath (and Tyrael's Might) are level 87, whereas Pindleskin is only mlvl 86. Meph is mlvl 90. So Pindle can't drop those things while Meph can (not Tyrael's, but that is because of Meph's TC, not his mlvl).
Now, in 1.09, high-end unique levels tended to be low enough that if a monster could drop the item type, it could almost always drop the unique, so this never came up. But it is here with bells on in 1.10.