Dragon Invasion Late Game Community Guide

Dragon Invasion is more or less a "solved" event at this point. That is, the community has pretty much figured out the best strategy to do well in the event. Follow this guide in order to understand how you can build a good formation to do well in the event.
Special thanks to Khaly, Laeliel and StormB as well as everyone else in the community participating in discussions that helped me understand the "magic" behind this formation which I am now just putting in writing here.
Notice that like everything else in the game, it is essential to understand the core of any formation and the strategy behind. Since very few players have everything in the game at their disposal, it is important to be able to adapt - someone else's "best" formation might not work for you unless you possess the same units, emblems, etc., developed at the same level.
Finally, this guide is for the "end game". Since it relies on some key elements, this might not work for you at all until later in the game (level 80+). But you can still apply the principles from here to conquer dragon invasion at your level.
=Key Points=
The goal of Dragon Invasion is to do as much damage as possible in the 1m 30s of battle. The more damage you do, the higher you will rank in the leaderboards, and therefore the better the rewards. 
In general it doesn't matter if your units survive for the entire battle or not, though the Azure Dragon is not a particularly high-damage boss, and therefore you will most likely not have to sacrifice too much aggression for survivability.
With this strategy you will notice that a lot of the damage is outputted in three stages: maybe more than half in the first 30s, then a large portion in the second 30s window, and then the last pieces in the final 30s.
==Understand the Dragon==
Go over the dragon's abilities and understand how they work as they will influence your performance. Probably the most relevant is the silence inflicted on your units after 30s and then after other 30s - it will temporarily debilitate your team by putting a hold on your units' skills. Some skills are more strongly affected than others, but once again this is a trial and error process to figure things out. Just keep this in mind!
And don't forget you can always reset the battle without losing attempts. Before the 30s count is reached, just forcefully close and reopen the application. It takes a bit of time (more than resetting Crypt for instance), but this will save you the attempt and also persist the previously used formation. So it's possible to do as many trial and error attempts as you want during a single event, and then just stick to your best option.
=The Core=
Out of all options, Gelu with Wood Elf and Marksman (referred to as "the archers" in this guide) can output the most damage against the Azure Dragon and are therefore the core to this strategy. There are no substitutes here - luckily all three are easy to obtain and grow, so this shouldn't be a big problem.
It is very important to get Gelu to 4* and Spell Mark him. We will look at options later on, but this is crucial to maximize damage. You can buy his tokens in the Champion Store so you won't have to invest your hard-earned Universal Hero Tokens in this direction.
Next, you want well-grown archers. Both are cheap units, available in very many places, but of course starting work on them early will help you tremendously (and they are useful PvE units even outside Dragon Invasion). Keep them to your Player Level, rank them up and don't neglect their awakenings. 
*Barracks, Wishing Well, Underground, Archery Expert are all sources of unit tokens
*You will need to get Grand Elf and Master Archer tokens from Plane Store and Arena Store - so of course doing well in Conflux Plane and Arena will allow you to faster get them to a minimum 5* awakening.
=The Strategy=
The approach is deceptively simple: build your formation in such a way that your archers output the most damage possible. There is no point in thinning out your formation with more units in a damage dealer role - they simply won't be able to get even close to what the archers can do. So you can already forget about any pure DPS units (Giant, Naga, Red Dragon, Hydra etc.) as they have no place in this strategy.
So how can we improve the damage output of our archers? Let's take a look at some concepts one at a time and start applying them them to build a formation.
==Unit Stats== 
If you went through the Damage page already you probably noticed that there attacker and defender stats. To maximize our archers we have two options:
*Stat boost on the archer units - unless the effects of your formation units don't benefit the archers but the units themselves, they can be ignored. Go through the pages of each stats for comprehensive list of effects in this direction - we care about "self" effects on the archers, and "bestow" effects on the other units.
*Stat decrease on the dragon - obviously negative effects affecting the dragon will decrease its damage dampening capabilities. There are plenty of effects in this direction - once again, please consult the pages to identify the best effects for you.
With this in mind, it becomes clear that for instance you don't want other units with Defense Penetration - this won't benefit the archers.
On the other hand decreased Unit Damage Reduction and Defense penalties will definitely improve archer damage.
Which of the stats work better and in what percentages depends of course on the stats of the dragon and your units, so it's impossible to give a global recipe here. Since we don't have the numbers on the dragon, it's also heavy trial and error. StormB ran extensive tests in this direction and his analysis suggests that Unit Damage Reduction is much more potent than -DEF, but it's best you test this for your own formation as well.
==Other synergies==
Your archers have another important common denominator: their Double Strike abilities. If you can guarantee a trigger chance, it will have an increase from 24% (level 15) to 100%, which in essence quadruples the effect. Therefore it is important to bestow slow on the Dragon as often as possible. 
==Survivability==
Don't forget your archers have to survive. This is achieved via some form of healing. If you have a strong Medical Tent or Rune Stone, it can be sufficient to keep you archers alive (and not lose figures - this is also very important!). But otherwise, you need a form of healing and/or Magic Resistance on your archers. Don't overdo it though, or find units that can touch multiple synergies, as the Azure Dragon is not a particularly high damage dealer.
==Casting Spells==
Gelu's spells arsenal is specifically tailored to benefit your archers. Precision and Frenzy work exceptionally well to generate huge bursts of damage from your archers. Spell Marks should also not be neglected as the right choice will also further boost your archers. Of course for all of this work, you need to group your archers together (on the same line) so your buff spells cover both units (yes, covering each individual figure in the unit is important).
Personally I like to boost the archers when outside periods of silence, as that way they synergize better with all your skills and effects (that are otherwise suppressed while silenced). Also overlapping Precision and Frenzy seems to be even better. Roughly you will be able to cast a Frenzy every other Precision.
=Choices=
Now that we spoke about the general strategy let's take a look at options. We can then finally put everything together in a sample formation.
==Archers==
The awakening skills are up to you but try to favor effects that maximize damage to effects that add survivability.
For Holy Emblems, you can go for any DPS emblem, but tests clearly show at this point that Path of an Assassin is by far the best option (even as a purple set, in favor of maybe other orange DPS emblems like Aksoe Token). But of course in the absence of PoA you can direct your attention towards what you have.
==Slow Synergy==
If you have a unit that applies slow often enough, it's probably all you need - I wouldn't overdo it with multiple effects. The most popular choices here are:
==Supports==
There are several units that can support your archers - and again, I don't recommend more than one pure support unit. Out of all, the best options by far are Genie and Silver Pegasus, as they both add survivability as well as act as either buffers or debuffers. Other potential options here are Mermaid and Zealot. 
You want to be careful that the buffs benefit the archers though, so in the case of Genie (due to Three Wishes) you will have to play quite a bit of shuffling games in your formation until the red and green buffs land on your archers.
==Debuffers==
By far this is going to be the most impactful category of units - the more of these you can fit into your formation (assuming your archers survive), the higher will your final damage be. The most relevant are as I previously mentioned the anti-Unit Damage Reduction effects. You want the unit skills to be as high %, consistent and durable as possible. Of course there is some optimization here to be done and that's trial and error you can always do.
So depending on what you possess here are some good options to consider: Bone Dragon, Nightmare, Revyaratan, Black Knight (with Lord Haart global ability), Spartan Warriors, Unicorn, Scorpicore, Silver Pegasus, Silent Snow Spirit. 
Finally don't forget Darkness Enlightenment also reduces a target's Unit Damage Reduction, but it doesn't stack beyond 50 times regardless of how many units target the dragon. Some people stick it to only one unit, while others prefer it on two to stack it up faster. Note that it triggers for each figure in a unit, so it's most potent on 9-man units. (never put it on your archers though!)
==Spell Mark==
There are quite a few options here, but the community agrees three spells in particular are most potent here (listed from the best to worst):
Of course Rush Tactic is more expensive, so if you don't possess it or it's at a very low level (hence you can cast it only 1-2 times), you can look at the next available option and so on.
==Emblem Choices==
So far we identified two PoA sets on your archers. We know we still want one or two Darkness Enlightenment sets and then we can focus on improving the skills of your support and debuffer units using Everlasting Secret or Anger.
We are aware that this is probably the most annoying part 
===Anger vs. Everlasting===
If the ultimate does not contribute towards debuffing, we already know Anger is not an option for the unit.
Everlasting Secret is great, assuming the coveted debuff effect scales - a counter-example is Nightmare's Dreamcatcher whose debuff effect does not scale with skill level. There is no point in putting Everlasting Secret on him.
In some cases both can be considered - Bone Dragon is a great example. Some people reported Anger is better, while others didn't notice really a difference between either of the two emblems.
===Remaining Options===
Once you have placed the previous emblems, you will most likely get one or two units that can fit Darkness Enlightenment. If after this step you still have units without emblems, doesn't matter what you put on them. For example my Dendroid Soldier still has its Successors' Legal Principles on it but I wouldn't say it makes a significant difference.
==Roster==
Don't forget to optimize your Roster. The page includes a link to my optimization tool. Keep in mind that here you want to give your archers the best boost possible - but your other units will also benefit from rosters as it increases their survivability.
=Example Formations=
Let's put everything we talked about together and get some formations. I will include two examples: a f2p and a luxury formation. They are by no means universally best but should give you a great starting point.
==Free to Play==
							
							
Here are the relevant support skills you will want to maximize (or choose when it comes to awakenings):
==Luxury==
							
							
In this case having a 2* Lord Haart is very important or else Dread Knight won't make the cut.
=Closing Statement=
Hopefully following this guide you have a much better understanding of Dragon Invasion now. Read this a couple of times, feel free to come back to it, and take your time to experiment with the best formation you can come up with.
May your dragon slaying be fun and fruitful!
Category:Guides