Before I get started, I want to say it's hard to explain each step of the tactic. Mainly because there are so many variables in a match (Ex: Early Magikill will ruin this tactic) that could make this tactic work or not work. This applies to every other tactic I make.
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Duration: 9:02
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The most smallest map is the map called Castle. This map is just as annoying as burnt toast because we don't have time to build our armies and we have to think fast since the Central Tower is just a couple feet away from our base.
But! I have found a solution! It may annoy your opponent, but this tactic worked for me (I only did this once though). :o
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Part 1, The Beginning:
We got our 2 miners near our base. So what should we start with? It's up to you. Personally, I would start with 1 Sword and 2 Miners.
<--- 2 Miners, 1 SwordDo not worry that your Swordwrath will be outnumbered by your opponent's. When your opponent rushes, I want you to buy a Castle Archer immediately.

Part 2, Annoy Your Opponent:
With your Castle Archer in your base, you basically rule 1/3 of the map already! :o
We are making great progress. If your opponent is staying at the Central tower, what I want you to do is to lure your opponent's army into your base. Use your Swordwrath from the beginning or buy another one (It's cheaper than an Archidon). I want you to keep doing this until he puts his army on hold.
If your opponent has an Archidon, then I recommend you to buy a Spearton or use your own instincts.
Lastly, buy a Miner Wall. This will signal your opponent to never ever rush to your base.
Part 3, Preparing to take back the Central Tower:
Alright! I want you to buy an Archidon. Archidons are devastating in short maps like Castle. Their range is almost 1/3 of the map already.
Continue to do Operation: Annoy Your Opponent. If your opponent still has an Archidon, then I want you to buy more Archidons! When one of your Archidons is dying, put him in garrison. Continue to do this until your opponent puts his army on hold or you successfully lured him into your base (With his army destroyed by your Castle Archer).
It's not safe yet to take over the Central Tower, because although your opponent would have retreated after losing most of his units, I want you to wait.
Buy more Archidons.

[Optional] Research Fire Arrows (Longer Distance to threaten your opponent's miners)

Then hire a Spearton.

Next, research Spearton Wall and Spearton Bash.

Recruit a Meric to heal your units.

Last but not least, research Ghost Tower 1.
Part 4, Operation TAKE OVER CENTRAL TOWER:
Alright, so before we begin, let's be sure you have everything.
You must have:
- A Miner Wall
- A Castle Archer
- 2 or more Speartons
- 5 or more Archidons
- [Optional] Fire Arrows
- Spearton Wall and Spearton Bash
- 2 or more Merics
- Ghost Spawn Tower 1
If you have all those things, great! It's time we take over the Central Tower.
There are 2 Scenarios:
1. Your Opponent's army is still sitting at the Central Tower
- Threaten his army with your Archidons. Fire Arrows are even better. Most likely, your opponent would retreat.
or
2. The Central Tower still remains empty.
- His army isn't there. He must have retreated.
If no one is at the Central Tower anymore, fantastic! Command your 2 Speartons to rush to the Central Tower, then command them to put up their shields. This will protect your Archidons from your opponent's Archidons. If everything works out right, you successfully took over the Central Tower! ;)

Part 5, Time to Win:
Remain cool! Do not panic! Since your Speartons are still in the Central Tower, quickly command the rest of your army to support the Speartons. Command your Merics and Archidons to the Central Tower.
This is the end result:

So now what do we do? Simple, do what you have to do to win.
Is there a Castle Archer in your enemy's base? No?

Kill his meeners!

Did your Ghost appear? Yes? Charge!

Win!

I hope you guys would use this tactic and win lots of battles in short maps like Castle! :o