You can only get all rare and super rare character pieces from the 75k packs. There are legendary stickers which are very rare in the 15k and 35k packs. There is the computer scientist, toxic brainz, disco chomper, and iron citron. You can get the party legendary characters from infinity mode which are the corn, rose, citron, imp, pirate, and super barinz.
This response was totally unhelpful. As the original post stated, the 75k character pack is no longer available, completely missing. No character pieces are in the other packs any longer. We have bought a zillion of them. Not one single character piece. We are still missing many characters, so how are we supposed to get them?
OP said he has around 10 characters missing, which corresponds with the amount of legendary characters there are. As such, (and as indicated by the fact that the response was accepted as a solution), OP was likely simply not aware that he/she had collected all he could from the 75K packs. Once you have collected all rare/super rare characters, there is nothing left to get from the 75K packs so they are no longer available to buy. The remaining 10 legendary characters are either only obtainable as a reward from Infinity Time or can very, very rarely be gotten from a 15K or 35K pack.
If you are indeed having a problem where there's rare/super rare characters left to get and you are not getting any stickers, then that's a different problem entirely. No need to call a response "unhelpful" when it was addressing a completely different issue 🙂
