War of the Guilds

War of the guilds, guild wars, guild verses guild, or GvG is an event that lasts for 27 days. The objective is to gain more kill tallies than your opponent. Kill tallies are racked up by members of your guild attacking an opposing guild's defending team. If all members of the defenders are killed the result is five kills. Each person has two attacks per day, and this means there is a possible of ten kills total.

Some points to remember:

If you're new you, and this is your first GvG you have to setup your defenders. Use wardens if you have them. Use your most powerful cards if you don't have wardens. Use hammers to increase the defense of your defenders.
Opposing guilds are awarded kills for vacant spots with in the guild (i.e., 28/30 means there are three vacant guild member slots, and so the opposing guild is awarded 3 x 5 kills, or a total of 15 kills).
As you participate in the event you gain an emblem. One emblem is awarded per attack on a defending team, and a win is not required to receive an emblem. As you gain emblems you use them in the Collection area to attain needed inventory items.
Warden souls are used to buy wardens. It's called forging in the Collection area. Once a warden is "forged" (i.e., purchased) the souls are removed from your inventory. Only 6 star (6*) wardens are of value, because the lessor wardens take too much resources to evolve, and you get better wardens on random card draws. You need 250 warden souls for a 6* warden, and you'll be able to get that many over multiple events. Warden souls are not removed from your inventory after an event.

Tips and Tricks

Here are some tips and tricks you can use to in GvG:

Set up your defenders! New players that join after the event starts, or who miss the "Set up Your Defender" announcement, may not know how to set up defenders. To set up your defenders click on the Rank button in the upper left of the Play screen. Slide your team First Team right. This is your defender area. The only relics that can be used here are defender relics (e.g., hammers). The defenders you want to put here are warden cards (your most powerful). Until you get a full set of wardens use your most powerful cards.
When attacking it's important to kill all five defenders, because that gives the guild the most points. So if you use one of your attacks and only kill three defenders don't attack the same person again. Attack another person to kill their five defenders. This gives the guild 8 kills instead of only 5 kills if you attacked again.
Select a team of defenders at or above you GvG attack team's power.
If two defending teams have the same power, and one has wardens, and one doesn't, the one with wardens is much more powerful. Use caution when attacking a team with wardens. Some times you have to select a lower power team than your attacking team if the defender's team has wardens on it.
Try and select a team of defenders which starts with a card that your attacking team has advantage on (e.g., attacking team Fire affinity, defending team's first card Earth affinity).
Test to see if you team can beat the defending team by using the Skirmish feature. I've set this video at the point where T Bone shows how to do a skirmish.