In these you are presented with arrows to shoot at a target. Each shot results in eliminating one target and you may also receive a amount of XP and cash from a random band. Higher level Hunter challenges may also give an enhanced payouts which includes 5FP (I recently had a Hunter Challenge which paid out an enhanced payout twice but this is very rare) as well. On completion of the challenge you are awarded an inventory item (which forms part of a set), cash and XP.
This is based more on a gambling theme. You are given chips and with them you have to win a high-low gamble a certain number of times. You may bet 1, 2, or 4 chips per gamble the more chips you bet on a hand the bigger the single payout for it, if you win. As well as the expected payout you will sometimes be awarded an enhanced payout of cash and XP. On completion, as with Hunter challenges, you are awarded an inventory item, cash and XP. In addition to these you are awarded favor points.
At the time of writing there are 3 Calendar Challenges: a monthly, weekend and weekday version.
Calender/Holiday challenges can only be repeat a set number of times (up to 3 times) within their time limit. You have 25 panels to reveal before you can finish a challenge and get the Clear Bonus. As well as the Clear Bonus each time you reveal a panel you get a reward of coin and XP based on your level and income:
Chance of Payout
x Gross Income
%age of Level XP
These challenges only used to be available on special occasions triggered by special annual events on the calender: Easter, Halloween etc. (hence the old name holiday challenge) but from January, 2011 the monthly calendar became a regular feature.
For each panel you wish to reveal you have to use a key. You receive a free key a set time after using the current free key. On top of the time based free keys you can also ask your clan for Free Shot keys. It requires the help from 5 Vikings to create a Free Shot key. You can have a maximum of 3, Free Shot keys at any one time. As a last resort it is also possible to buy keys at a cost of 3FP per key. There is no restriction on the amount of keys you can buy so in theory you could complete a challenge at once by spending 72FP on 24 keys. (You would only need to buy 24 as you get a free key whenever a new holiday challenge starts.)
This is the oldest of the calendar challenges. As the name suggests it spans an entire calendar month. You get one free key per day. This is the only Holiday challenge that may only be completed once within its time limit.
This challenge event is 72 hours long and spans 4 days. It can start on any day of the week but will usually start a Friday and finish on the Monday. It may be repeated up the 3 times within the time limit. There are usually about 2 of these events per month. Once started a new key becomes available every 30 minutes. This version of the calendar challenge is more likely to celebrate holiday than the other 2.
This is the most recent challenge event is 96 hours long and usually runs from Monday to Friday. It too may be repeated up to 3 times within its time limit. New keys appear every 45 minutes. (When the 5-day event first began free keys appeared every 50 minutes.)
An unusual feature of the Calendar challenge is the ability to post messages to other Viking Clan players, like the World Bosses. This used to be a good place to find new clan members as clicking on the names takes you to the Facebook profile page of that member but now it is much easier to do this using World Chat.
This may be a bug, but (at least with the weekend Holiday Challenge) it is possible to use keys after the event has finished (but before it disappears from the Challenges list). This may also be possible with the monthly and weekday challenges as well but I have not tested those yet. What is really surprising is that you can also buy keys after the event has ended. Using these keys will definitely give you extra XP and coin but I do not know if this will give you the Clear Bonus.
When you help other players' with challenges, you are awarded a small amount of XP which equates to roughly 1% of the XP you need for your current level. This is limited to 50 Hunter / Odin's Rune assists per 24 hours. After that, the XP reward is reduced by 0.04% of your current level requrements until it reaches 1 XP.
Example: If you need 50,000 XP total to achive your next level, the first 50 challenge assists will each pay 500 XP. The 51st will only pay 480 XP, the 52nd will pay 460 XP, the 74th will pay 20 XP, and the 75th and all subsequent assists will pay 1 XP. Once the 24-hour period has elapsed, the payout returns to 500 XP.
Note that 3-day calendar assists pay only 1/2 the XP bonus (in the example above, that would be 250 XP) but fully count toward your 50-assist limit.
Note that monthly calendar assists do not count toward the 50-assist limit and pay the full 1%-to-level XP bonus.