In Clash Royale, Mirror is a card that is just shy of being an underrated card, being just barely underpowered yet still quite useful in many cases…
A guide by yojojo3000
Mirror Summary
The Mirror allows you to place the previous card you just played into the arena, allowing you to play 2 Hog Riders at once, 2 Skeleton Armies at once, etc.
The Mirror will cost the same amount of elixir as the previous card you played plus one more elixir, which means that if you were to Mirror a 4-elixir Hog Rider, the Mirror would cost 5 elixir to use, and if you were to Mirror a 1-elixir Ice Spirit, the Mirror would cost 2 elixir to use, etc.
The lowest the cost of the Mirror can currently go is 2 elixir, and the highest the cost of the Mirror can go is capped at 10 elixir.
On top of that, the card that your Mirror places will be one level higher than the Mirror’s level, meaning that a Level 9 Mirror will place a Level 10 card every single time, and a Level 13 Mirror will place a Level 14 card every single time, regardless of which card you use the Mirror on.
Strengths of the Mirror
Conceptually, having a Mirror in your deck can definitely be a lifesaver in some situations.
Against Bait decks (decks that revolve around forcing a certain card out of your opponent’s hand in order to allow another card in your deck to reach the tower without having to worry about said card), Mirror can counter their strategy pretty hard. Their goal is to force a specific card out of your hand in order to reach the tower, but with Mirror, you basically have two of said cards in your hand. This makes it really difficult for the Bait player to get to your tower.
Ironically, Mirror pairs quite well with Bait decks as well, though arguably less effective than using Mirror as a counter card due to the higher elixir cost of the Mirror. It basically gives you an extra card to bait cards with, or allows you to counter spells like Zap on your Skeleton Army.
Mirror can be particularly strong if used to Mirror powerful cards such as Sparky, Giant Skeleton, Battle Healer, etc.
However, due to the massive elixir cost of most of these powerful card, finding yourself in a situation that will allow you to Mirror said cards safely is, to put it quite frankly, niche. I wouldn’t rely solely on just that strategy to win, but you can sometimes squeeze it in your deck just in case the opportunity arises for you to make use of it.
Pairing the Mirror with win conditions such as Hog Rider and Giant is questionable and very risky, but if you can play the game just right, just so perfectly, you can get away with giving your opponent 9 elixir, 11 elixir, whatever in exchange for their tower.
But again, it’s very risky and not for beginners or even intermediate players.
Weaknesses of the Mirror
This one weakness alone is probably why the Mirror is so underpowered at the moment:
Mirror places the previous card played, and only the previous card played.
What does that mean? It means that it’s exploitable.
If you have a Mirror ready to Mirror a Mini Pekka for their Hog Rider, they could instead play Skeleton Army at the bridge and force you to play something else, like The Log. Because of that you lose the opportunity to Mirror your Mini Pekka because now the Mirror is set to Mirror the Log you just played, which means that they are free to play a Hog Rider and get damage on your tower.
Faster cycle decks can easily get around the Mirror by exploiting this. By using their cycle cards, they can easily force you to play something else before they get back to the card that you want to stop.
Even Bait decks can exploit this consistently. A simple Knight or any tank can force you to play something else and cause you to lose the opportunity to use the Mirror as it was intended to be used.
Against less knowledgeable players who don’t exploit it intentionally or unintentionally, you’ll probably be fine, but at higher Ladder, this exploit is gonna be abused a lot.
Another weakness is the +1 elixir cost of the Mirror.
You might think “oh it’s just one more elixir, how bad could it be?”
It’s actually pretty fatal.
Mirror is very prone to making negative elixir trades (based on my own experimentation) and I guess it’s just because it’s all so expensive. Even without the +1 elixir cost it would still be very prone to negative elixir trades. This makes Mirror quite difficult to use.
How to Use Mirror
Due to the limitations and weaknesses of the Mirror, the best way to use the Mirror is as a backup card (replacing what was destroyed) or a counter card (destroying what was replaced).
The downsides of the Mirror make taking risks unfavorable until you can guarantee that you’ll be safe when making a risky play with it, so you’ll mainly be using Mirror in non-risky ways, such as being a backup or a counter card.
Because of that, don’t expect to use your Mirror often during a match. Sometimes you’ll go an entire match without using the Mirror once, so don’t force yourself to use the Mirror.
Only use it when it becomes relevant.
A good way to practice your patience with the Mirror is to try to win the match while using Mirror as little as possible.
Once you work up a large enough elixir lead on the opponent, feel free to make risky plays with the Mirror, such as Mirroring win conditions or making offensive plays with the Mirror.
You’ll want to have strong synergies with your Mirror so that you can actually use Mirror to its fullest potential.
Having at least 3 cards that synergize with Mirror makes for a good deck.
Good synergies include strong units that easily die to spells like:
Any spell, strong counter cards like:
Strong counterpushing cards like:
And cheap and/or strong win conditions.
You have a very wide selection to choose from, but make sure that it works for your deck.
You’ll also want to try making your deck just a tad on the cheaper side.
Without Mirror, your deck can have an upwards elixir cost average of around 4.2 elixir before becoming too heavy to be viable (unless you use Elixir Collector), but with Mirror, I’d say your deck can only have an upwards elixir cost average of around 3.8-ish 
elixir before becoming too heavy to be viable (unless you use Elixir Collector).
The +1 elixir cost of the Mirror can really hurt you, especially if the Mirror is likely to be sitting in your hand most of the game, because there may be times where you only have 2 elixir in hand stuck with a full hand of expensive cards, and then the opponent plays a Hog Rider at the bridge and gets 5 shots on your tower by the time you are finally able to place something.
That said, Mirror works pretty good in cheap decks as it allows you to use the Mirror more often and with far less punishment, though you run the risk of having a weak offense as well.
You gotta find the right balance between cheap and expensive.
Common Mirror Pairs
Goblin Barrel — Goblin Barrel is a disgusting card to Mirror. With the combination of having very few counters and a cheap cost, the Goblin Barrel is the most common card you will see paired with Mirror as it allows you to be very aggressive on the offense.
Bats/Skeleton Army — A defensive competitor of the Goblin Barrel, Skeleton Army and Bats are also known to be common pairs with the Mirror. Both can do insane work on defense if left to do so, and spell counters such as Zap or Giant Snowball can be heavily negated with the Mirror spell. However, a Poison spell can absolutely hard-counter this strategy, so be careful when you face someone using Poison!
Valkyrie — It’s no surprise that Valkyrie is commonly seen with the Mirror. This woman can absolutely nuke pushes. What if one Valkyrie isn’t enough? Have two Valkyries! What if two Valkyries aren’t enough? Well, you’re screwed.
Spawners — Probably the most irritating synergy of them all and unsurprisingly another common sight, spawners benefit a lot from the Mirror, most notably the Furnace. Though expensive, it can prove to be worth the extra cost if your opponent doesn’t have two answers to your spawners. This can force opponents to push into your spawners in order to prevent chip damage on their towers, which is exactly what you want them to do. Just be careful about spending too much elixir to get them.
Damage Spells — Probably up there with Goblin Barrel for understandable reasons, Damage Spells of any elixir cost are great pairs with the Mirror due to their extremely versatile nature, allowing you to chip down or even nuke pushes with ease, or even finish the opponent’s tower twice as fast. Need I say more?
How to Counter Mirror?
3 words: Abuse The Exploit.
Make them cycle cards they don’t want to cycle before playing your desired card. This directly counters their counter to your desired card.
In the case where the opponent uses Mirror as a backup card, Mirror can be a tough brick wall sometimes.
If brute force can’t break through the opponent’s Mirror, applying pressure in both lanes will.
If the opponent plays his backup card in the opposite lane in an attempt to stop both sides, clearing out one side will almost ensure that you will get good damage in.
If he doesn’t play his backup card in the opposite lane and decides to play his backup card in the same lane (stopping your push), the opposite lane will get good damage in.
For the opponent, the best he can do is to not use his Mirror and try to defend both lanes with other cards.
The most important thing to do against an opponent with Mirror is to not let the opponent get an elixir lead on you. If he gets an elixir lead on you, he will cash in that elixir lead with an offensive Mirror, which will likely prove to be fatal if you’re not prepared.
This guide has been brought to you by u/yojojo3000
