You can raid other players' towers and earn trophies, gold, training points, and loot drops. Each time you are paired up with an opponent you either have the option to attack it, or refresh to get another player if the tower/rewards aren't desirable.
You have one hour to attack that player before it automatically refreshes, or you can pay 3 gems to manually refresh it for another opponent. Every time you refresh manually, the next time you refresh will cost more gems if you haven't attacked a tower in the meantime.
If successful you get random loot drops equivalent to half of the floors that tower had, rounded up.
The gold earned from a tower is equal to the sum of all tower defenders' levels * 1.25. (roughly tower rating * 18.5).
Prestige earned is equal to the tower's rating. Tower rating is equal to the sum of all tower defenders' levels / 30, rounded up, then multiplied by 2. This would make the highest theoretical tower rating equal to 160 (max 3k gold reward).
Prestige earned from a successful tower defense is your own tower rating divided by 2, plus 10.
Always equip good potions, skills, max-level weapons and armour. Don't enchant good gear until lvl 51 during Dragon's Hoard to get maximum benefit (save at least 2M gold for this festival event). Use item boosters to save on resources.
A good all-rounder team: Edit
Gear and skills for this team at level 45: Edit
For Warlock: Demonfire/Acid Bolt, Ball of Darkness, Drain Life. Shadow Wall, Dark Patron passives
For Druid: Entangle, Cyclone. Heal: Renewal. Heart of the Wild, Essence of Nature passives
For Knight: Threaten, Sunder(pairs nicely with Druid attacks), Parry. Courage, Enhanced Armor passives
For Cleric: Righteous Call(doubles as heal and attack), Powerful Heal(because), Cleanse(explains itself). Healer, Charismatic Leader(gives a nice boost to all resists) passives
Team for pretty much any level(IF you're slow-levelling) Edit
This team should work almost anywhere, anytime--WITH sufficient stars and gear
Meta Team for well-prepared 55s Edit
Gear and Skills: Edit
Skills for Warlock: same as above
Skills for Mage: same as above but maybe use Acid Lance instead of Zap
Skills for Templar: Challenge Evil, Punish the Wicked, True Strike. Resistant, Divine Favor
Skills for Cleric: same as above
Lvl 55 Valkyrie Front Strat Edit
Gear + Skills: Edit
(Barbarian is flexible: any Epic tier armour should suffice) + King's Hammer
Piercing Blade + Plate of Undeath
Piercing Blade + Chain of the Wretched
King's Hammer + Keldis' Raiment
Skills for Barbarian: Whatever works, though Leaping Strike doesn't take damage from Thorns or Blade Barrier as well as being able attack the back-line directly, so there's that. Bear's Strength is great with Weapon Throw. Whether you choose Savage Swipe or Turtle's Shell obviously depends on if you're going full offence or part defense. Owl's Insight and Hawk's Speed are both incredible, so try to use them together. If going defensive, use Ward instead of one of the other passives.
Skills for Blackguard: With the aforementioned plate, Blackguard can go all out offensively and still retain full benefit. Vicious Strike and Double Swing, cause everyone uses that; Death Glare, because FULL OFFENCE! Passives: Find Weakness, Deadliness.
Skills for Valkyrie: Shield of Yreth, Light of Yreth, Angelic Volley. Passives: Wild Storm and Fire of Yreth('cause why not go down damaging?)
Skills for Cleric (oh, this is monotonous): same as above
Berserker floors will be annoying: either stack Inspiration and/or another defensive/armour buff before you attack, or try and destroy the Berserker directly before he kills or disables you.
Ninja floors are really annoying, so use either a hero which provides high defensive and/or resistant stats plus maybe a Druid or Witch for much better healing.
RARELY, you may face a good Cavalier floor. These are annoying because they require you to either highly buff your defense and/or armour, or destroy the Cavalier. Luckily, all that attack comes with a defense penalty, making it much easier.
Often, you'll run into a Blackguard floor. These are some of the most frustrating floors around-especially if the Blackguard is high-starred and/or on a well-equipped floor. Nothing really for it: a good high-starred, well-equipped team with Cleric plus potions is usually needed to beat this.
A Valkyrie floor is as annoying as the Blackguard at high stars. Try not to use stun, fire, or lightning against her if she's highly-starred: the Wrath of Fire skill reflects these as fire damage. Her soul does fire damage increased by -and also removes- armour.
A Samurai floor is less annoying: bring a Cleric and/or Mystic to remove the debuff from your damage-dealer.
A Swashbuckler has a high amount of dodge, owing to his skills. Wait 'till he uses Balestra before attacking with a DOT skill, and equip non-dodgeable skills to make sure of a hit.
The Templar can make a floor take nearly twice as long (he can't resurrect walls or himself)
Amazon floors are slow-going sometimes, Cover Allies reduces damage taken--of any sort. They can be either defensive or offensive until level 55, when they're both.