You will need to purchase and build a Laboratory in order to upgrade any of your troops but in order to upgrade your troops the price will be elixir regardless of whether it's the regular elixir or the dark elixir. The Laboratory can be upgraded like other buildings can which will allow you to unlock additional levels for troops however only troops that you have unlocked will be available for upgrading. Spells can also be upgraded as well but you need to have the spell unlocked in order to upgrade it.
YEs, you can donate spells in Clash of Clans
Yes, you can donate up to five troops (depending on spaces) per request for troops. If the player requests troops, but the castle is not filled, they can request again in 15 minutes, and you can donate a second time.
no because you can only give troops
Healers will not heal flying units hence can not heal air troops.
eubie
There are no codes in clash of clans.
There is no "best" base in clash of clans.
No, Clash of Clans is not available for Nook.
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No, you must have an internet connection to play Clash of Clans.
No, Clash of Clans has not yet been made for the Kindle.
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