The Clan Castle's strong defending troops can make the difference between an attacker getting 3 stars against your village or not even getting a single star. They can also be used to protect your village from people looting your resources, but they are more important for Clan Wars, so make sure your Clan's Clan Castles are full during the preparation day.
There are several combinations of powerful troops that you can use in the Clan Castle. Below are some suggestions for each Town Hall level, along with an explanation of their strengths.
General information
Donate Max Level Troops- Try to make sure the troops are at maximum level. If your clan is at least level 5, donated troops will be increased by 1 level, and if your clan is level 10 or higher, they will be increased by 2 levels. This allows lower tier prefectures to donate higher tier troops.
Subordinate troops are better than no troops at all- When the preparation day is over and some clan castles are still empty, donate adequate troops even if they don't reach the maximum level.
variety is important- While it might be easier to donate the same troops to each clan castle, it makes it more predictable for the enemy to plan their attacks. If they know which Clan Castle troops will show up, they'll be prepared. Keeping them on their toes can give your clan an advantage.
Avoid filling a clan's castle with the same troop- There may be exceptions to this rule, but in general it's best to have a mix of troops in the clan castle. For example, if you only use balloons, they will appear and move at the same speed and direction as a group, making them easy to cover with a poison spell and take out troops with splash damage. A mix of troops moving at different speeds will make this difficult.
Make sure the clan castle can protect against air and ground attacks- If Clan Castle troops can only attack ground units, they are ineffective against air attacks and vice versa. Having a mix of troops to counter both types of attacks is key.
Consider the likely attacks the Town Hall level will defend against- Donate troops that are effective against attacks you think will be used against this Town Hall level. If you're anticipating Hog Riders or Valkyries, a Baby Dragon and/or Balloon can be effective in taking out groups of ground troops. If you are anticipating a LaLoon attack, a dragon or baby dragon can be effective in taking out groups of balloons.
Avoid mixing a baby dragon and other air troops- The baby dragon gains a 2x damage bonus when not near friendly air troops. So making sure you're the only air force in the clan castle will ensure that this damage bonus is always in effect.
Troop donation order does not affect deployment order- The order in which troops are donated to the clan castle does not affect the deployment order. Order Troops deployed are determined by lowest residence location first, then lowest tier first.
chickens
city hall 8
city hall 9
city hall 10
city hall 11
city hall 12
city hall 13
city hall 14
city hall 15
If you haven't upgraded your Clan Castle to the current Town Hall level, use the troop suggestions for your Clan Castle's available capacity.
city hall 8- 25 tropa slots
In Town Hall 8, the priority for troops defending the Clan Castle is damage, especially against the usual troop groups like Runners, Valkyries, and Balloons.
x1 x1
1 x Drache, 1 x Balloon- Runners, Valkyries or Balloons can be common attacks at TH8, and the initial damage of a Dragon and Balloon can quickly take down groups of attacking troops.
x1 x1 x3
1 x baby dragon, 1 x witch, 3 x archer- The baby dragon can be very effective in eliminating groups of troops. Witch spawned skeletons can effectively weaken Hog Riders or even slow down a low level Archer Queen from a TH9 attacker.
city hall 9- 30 tropa slots
In Town Hall 9, the priority is a combination of troops with higher hitpoints and damage, especially combinations that can slow or stop a Queen Walk.
x1
1 x Lavahund- A Lava Hound can be very effective in slowing down the enemy Archer Queen due to its high hit points, and the Lava Pups spawned can deal a significant amount of damage to it. Great for slowing down Queen Walks or the Archer Queen in a group of troops.
1 x Baby Dragon, 1 x Witch, 1 x Valkyrie- The baby dragon can be very effective at taking out groups of troops, the witch spawning skeletons can distract single-target troops, or the barbarian king/archer queen and valkyrie can take out groups of low HP troops/skeletons spawned by witches.
x1
1 x electrodrake- Electro Dragon can take a lot of damage due to its high hitpoints and can be very effective in taking out groups of troops like Bowlers, Hog Riders, Valkyries and can even defeat a mid-level Archer Queen (level 23 or lower) with a single hit of full health.
x1 x2
1 x dragon, 2 x balloons- The dragon has high hitpoints and moves faster than the clan castle balloons. This should result in the attacking troops targeting him first, while the balloons move into position and deal massive area damage.
Rathaus 10/Rathaus 11- 35 tropa slots
In Town Halls 10 and 11, a Queen Walk/Queen Charge can be a common start of an attack, so defending troops who are able to slow that part of the attack down can be effective. Groups of bowlers and witches are also common, so splash damage troops (such as a baby dragon) are good choices.
x1 x1 x1 x2
1x Baby Dragon, 1x Ice Golem, 1x Valkyrie, 2x Goblins- A baby dragon can be very effective when it comes to taking out groups of ground attack troops or balloons. The Ice Golem can keep attacking troops occupied/frozen, giving Valkyrie and Baby Dragon extra time to deal damage to the attacking force. Goblins may seem like an odd troop choice, but their high movement speed and relative DPS ensure they reach the attacking troops first and distract them while the other Clan Castle troops stay in range.
x1 x2 x1
1 x baby dragon, 2 x witch, 1 x archer- The witch spawn skeletons can be a huge distraction for attacking troops, while the baby dragon eliminates groups of troops with lower HP.
x1 x1
1 x Lavahund, 1 x Balloon- A Lava Hound can be very effective in slowing down the enemy Archer Queen due to its high hitpoints, and the Lava Pups spawned can deal significant damage to it. If the attacker doesn't have many DPS troops in range, the balloon will be in range of his troops before the lava hound is knocked out and he will be able to take out groups of ground troops.
x2 x1 x5
2 x Super Minions, 1 x Headhunter, 5 x Goblins- Super Minions are very effective to end a Queen Walk, as their first attack is out of reach of the Queen and deals high damage. If your attacker isn't prepared with a Freeze spell, he will quickly overwhelm you. The goblins leave the clan castle first, distracting the queen so the headhunter can poison her.
city hall 12- 40 tropa slots
In Town Hall 12, a Queen Walk/Queen Charge is still a common sight at the start of an attack, so it can be effective in defending against troops that can slow that part of the attack. AoE troops to take down groups of pigs, players, witches or balloons can also be a viable choice.
x1 x1 x1 x3
1 x Baby Drag, 1 x Eisgolem, 1 x Hexe, 3 x Kobold- A baby dragon can be very effective when it comes to taking out groups of ground attack troops or balloons. The Ice Golem can keep the attacking troops manned/frozen, giving the witch and baby dragon extra time to damage the attacking force. Goblins may seem like an odd troop choice, but their high movement speed and relative DPS ensure they reach the attacking troops first and distract them while the other Clan Castle troops stay in range.
x1 x2
1 x Lavahund, 2 x Balloon- A Lava Hound can be very effective in slowing down the enemy Archer Queen due to its high hit points, and the Lava Pups spawned can deal a significant amount of damage to it. If the attacker doesn't have many DPS troops in range, the balloons will be in range of their troops before the lava hound is knocked out and they will be able to take out groups of ground troops.
x2 x1
2 x Ice Golem, 1 x Baby Dragon- Ice Golems in the Clan Castle defense are very effective in slowing down an attacking force. Having your clan castle located at the bottom of your village will ensure that attacking troops are in range of multiple defenses while they are frozen. The high splash damage baby dragon makes it easy for groups of players and witches to work while it's frozen.
x3 x4
3 x witch, 4 x archers- Witches can be very effective in stopping a Queen Walk. If the attacker doesn't have a poison spell or has placed an evil one, hags can spawn skeletons at a faster rate than the queen can dispose of them. This can force the attacker to waste time, use the queen's ability prematurely, or have to send additional troops to support.
x40
40 x archer- Usually a large number of the same squad in the Clan Castle is not as effective as a mix, but with the higher capacity of the Clan Castle at TH12, so many archers can make it difficult to attract everyone into a single group. This can result in the attacker using a poison spell prematurely, leaving several archers in the clan castle ready to pop in later. Such a large group of archers can deal a huge amount of damage per second, which allows them to effectively defeat heroes and other troops.
x1 x4 x4
1 witch, 4 headhunters, 4 goblins- This can be a powerful counter to a queen or guardian walk. The Goblins will be the first troops to leave the Clan Castle, followed by the Headhunters and lastly the Witch. Goblins can distract the Queen or Warden, allow Headhunters to poison them, and can force the ability to be used early or even disable them.
x2 x2 x4
2 x Super Minions, 2 x Headhunter, 4 x Goblins- Super Minions are very effective to end a Queen Walk, as their first attack is out of reach of the Queen and deals high damage. If your attacker isn't prepared with a Freeze spell, he will quickly overwhelm you. The goblins leave the clan castle first, distracting the queen so the headhunters can poison her.
Rathaus 13/Rathaus 14- 45 tropa slots
Town Hall 13 sees similar attacks to Town Hall 12, with groups of Pigs, Miners and Yetis being common. It can be effective to slow down these groups of troops to give high-damage defenses more time to attack them.
x3
3 times by Eiskole- Ice Golems in the Clan Castle defense are very effective in slowing down an attacking force. Having your clan castle located at the bottom of your village will ensure that attacking troops are in range of multiple defenses while they are frozen. With 3 Ice Golems, attacking troops will be pinned down under defensive fire, which should result in KOing multiple troops.
x1 x1 x1 x1
1 x Baby Drag, 1 x Ice Golem, 1 x Witch, 1 x Valkyrie- A baby dragon can be very effective when it comes to taking out groups of ground attack troops or balloons. The Ice Golem can keep the attacking troops occupied/frozen, giving the Witch, Valkyrie and Baby Dragon extra time to deal damage to the attacking force.
x3 x9
3 x witch, 9 x archer- Witches can be very effective in stopping a Queen Walk/Queen Charge. If the attacker lacks a poison spell or is misplaced, hags can spawn skeletons at a higher rate than the queen can drop them. This can force the attacker to waste time, prematurely use the queen's ability, or send additional troops in support.
x1 x1
1 x Laundry Dog, 1 x Eisgolem- A Lava Hound can be very effective in slowing down the enemy Archer Queen due to its high hit points, and the Lava Pups spawned can deal a significant amount of damage to it. The Ice Golem will further slow its progress, potentially causing a "time error" on the attack.
x45
45 x Archer- As with the use of mass archers in TH12, with so many archers it can be difficult to get everyone into a single group. This can result in the attacker using a poison spell prematurely, leaving several archers in the clan castle ready to show up later. Such a large group of archers can deal a large amount of damage per second, which allows them to effectively defeat heroes and other troops.
x1 x4 x9
1 witch, 4 headhunters, 9 goblins- As with this combo at TH12, it can be a powerful counter to a queen or guard walk. The Goblins will be the first troops to leave the Clan Castle, followed by the Headhunters and lastly the Witch. Goblins can distract the Queen or Warden, allow Headhunters to poison them, and can force the ability to be used early or even disable them.
x1 x1 x3
1 x Ice Golem, 1 x Witch, 3 x Headhunter- This can be an effective combination against air attacks, as the witch and ice golem will distract the dragons while the headhunters attack the great guardian (or other heroes). This can cause them to activate their abilities prematurely, allowing Giga Inferno and other key defenses to do significant damage.
x2 x1 x1 x3
2 x Super Minions, 1 x Hexe, 1 x Headhunter, 3 x Goblins- Super Minions are very effective to end a Queen Walk, as their first attack is out of reach of the Queen and deals high damage. If your attacker isn't prepared with a Freeze spell, he will quickly overwhelm you. The goblins leave the clan castle first, distracting the queen so the headhunters can poison her.
city hall 15- 50 tropa slots
Defending troops that slow down the attacker or require quick reactions from them can be effective in Town Hall 15.
x1 x3 x2
1x Lava Hound, 3x Headhunter, 2x Archer- A Lava Hound can be very effective in slowing down the enemy Archer Queen due to its high hit points, and the Lava Pups spawned can deal a significant amount of damage to it. Headhunters reach them first and can sometimes knock them out if the attacker is not prepared.
x2 x2 x1 x4
2 x Superminion, 2 x Rocket Balloon, 1 x Headhunter, 4 x Archer- Super Minions are very effective to end a Queen Walk, as their first attack is out of reach of the Queen and deals high damage. If your attacker isn't prepared with a Freeze spell, he will quickly overwhelm you. The Rocket Balloons will reach the Queen very quickly and if the attacker casts a spell on them once they reach them, the Super Minions will likely be out of range.