I didn't see this idea in the sticky but sorry if its ruled out but here goes:
In many games that i play they have special rewards when they do specific tasks and they get an item that belongs to a collection. When you trade in this collection you get an in game reward like xP, currency, and perks
So i had a similar suggestion for CoC. If you do something them you get an item and you can try and get a collection
In supercell's benefit i thought maybe you could buy items depending upon how rare they are.
I came up with a few examples that could be suggested
Town hall:
So when you destroy a townhall, you havea chance of winning an item. In each collection there are five items and they go in ascending order in rareness. So the last item out of the five will be a lot harder to get than the first.
When an item is found, a picture will come up on your screen and also at the bottom of the screen will be the collection that it belongs to, this way you can check your progress. You can always check your progress at any time. Perhaps an new button could be added next to village edit mode.
Also some of the gem values may vary depending on the type of collection. If it is an easy colllection like the elixir collection then the gem values and rewards will be somewhat lower than those of a harder collection.
This is the order for a townhall
Chimney- a common piece from destroying the townhall and is worth 10 gems
Flag- second common and can be bought for 15 gems
pillar- 3rd item and can be bought for 20 gems
villagers hat- 4th common so this is pretty rare and can be bought for 40 gems
door- the rarest of this collection and is worth 60 gems
once you have all these items you are able to trade in your collection for a reward. Note you can only trade in a collection if ALL items are present.
So for the townhall the reward would be 1500 XP and 20-100 gems (feel free to suggest any other rewards and adjustments to the rewards)
So here are a few others i could think of:
Elixir harvester
this collection is specifically based on collecting from your elixir pump.
Elixir droplet- common and 30% chance to get this when you collect from your elixir collectors. Worth 10 gems
pipe- pretty common and 25% chance to get this. Worth 15 gems
bolt- uncommon and 15% chance to get. Worth 20 gems
screw- fairly rare and only 8% chance to get this. Worth 25 gems
elixir bubble- rarest on the list and only 2% chance to get this. Worth 40 gems
Reward when completed- 1d free boost (maybe) and 500 XP
The same principle applies for gold mines.
so here are some of the harder quests. Their collections are a lot more lucrative and offer better rewards but the items are more expensive to gem.
This collection applies to builder huts
saw- 20% chance to get this when destroying a builder hut. Can be purchased for 30 gems
hammer- 15% chance when destroying builder hut. Purchasable for 35 gems
builders jacket- 10% chance. Can be bought for 40 gems
toolbox- 5% chance. Can be bought for 60 gems
Materials- 1% chance and can be bought for 80 gems
reward for completion- 2000XP 40 gems and perhaps a perk?
a few notes. This is NOT a minigame. These items can potentially pop out when a building is destroyed and the collection can be redeemed at any time. A confirmation is asked when buying items to avoid accidental purchase. I understand if you think my rewards are a little too much and if you have any suggestions or alterations then they are appreciated. It would be great if you guys could give me a few ideas for more collections. Collections can be redeemed unlimited amount of times provided you have all the items belonging to that group.
thanks for taking the time to read and I would love to hear what you guys think :)

