Welcome to the guide detailing every single of the collector’s quests, as well as the rewards you can obtain.
Every day, you can complete 3 quests. They usually give somewhat minor rewards, but once in a while, you can gain platinum, dark Miscrits or even Miscrits that are unobtainable otherwise. When you have completed all the quests, you start over at the first one and can access the rewards a second time.
Here is the list of all the Miscrits you will need to give the collector.
WATER MISCRITS:
10 Hydroseal, 7 Snortus, 2 Waddles, 6 Nessy, 8 (9) Shellbee, 7 (8) Squibee, 9 Prawnja, 9 Wavesling, 19 Orcatide, 1 Dark Prawnja, 1 Snorkels
FIRE MISCRITS:
14 Sparkupine, 5 Flameling, 11 Lumera, 19 Steamguin, 5 Sparkitten, 1 Blazebit, 3 Whik, 1 Ignios
NATURE MISCRITS:
5 Cubsprout, 2 Quirk, 7 Snatcher, 8 Elefauna, 5 Twiggum, 8 Flowerpiller, 1 Treemur, 5 Grubbean, 4 Echino
EARTH MISCRITS:
6 Drilldent, 3 Mumbah, 10 Croaky, 8 Craggy, 9 Digsy, 2 Eggy, 5 Hippoke, 1 Quebble
WIND MISCRITS:
20 Equestrion, 17 Breezycheeks, 12 Aria, 3 Owlie, 6 Jack, 3 Leggy
LIGHTNING MISCRITS:
10 Statikat, 5 Kiloray, 1 Luna, 7 Jellyshock, 2 Sparkslug, 6 Sparkspeck, 1 Thundercracker, 4 Arigato
And here is the list of all the quests, in the order they appear, as well as the rewards for each quest.

Many thanks to jimmyowns2 and Panetex who helped me complete this faster than I would have alone. Hopefully this can help people on their quests and show them that they are worth doing.