The Skeletons are most effectively used to distract and/or swarm slow-targeting and/or single-target, medium to high-hitpoint units, such as Giants and Princes.
They are an amazing counter against Mini P.E.K.K.A. since he can be distracted very easily. However, people usually back up their Mini P.E.K.K.A. with an area damage troop like the Valkyrie, so be careful.
Despite this, the Skeletons will not be able to defeat most threats by themselves, unless the enemy troops are already distracted.
The Skeletons can be used to counter a lone Princess. If played just after the Princess fires, the Skeletons will eliminate her quickly. Be careful, as if they are played with bad timing, the Princess will easily eliminate the Skeletons with one hit.
Skeletons can be used to distract Sparky, but be careful as she is almost always supported with area damage cards. Also, Sparky herself does area damage. This can be remedied by deploying the Skeletons around her.
They can be used as kamikaze troops, providing an effective distraction while another card is played or the Crown Tower destroys them.
If the opponent places an Inferno Tower to counter a tank, Skeletons can distract the Inferno Tower for a short time.
For just one Elixir, the Skeletons card can cycle the player's deck quickly, and add a significant boost to an attack. Better yet, not many players are willing to do anything to a pack of Skeletons, so they will have to address the combo before the Skeletons.
Skeletons can be used along with certain other cards like Knight or Mini P.E.K.K.A. to easily counter Elite Barbarians. Use the Skeletons to bait the Elite Barbarians into the center then place down Knight or Mini P.E.K.K.A. to finish them off. This can then assist in a counter-attack.
The Skeletons are easily eliminated by an opposing troop, building or Crown Tower, especially area damage cards, so it is recommended to use them only for defending against and/or distracting opposing troops. However, they can be a small boost to a push if they're well protected and away from splash defense.
They can also be used to help cycle through the player's Battle Deck to a desired card faster, as they have a very low 1 Elixir cost. This can be used to create powerful attacks (e.g. 2 Giants or 2 Witches.)
They are very similar to Goblins, but Goblins have slightly better stats in every way except troop count for 1 extra Elixir.
Skeletons was released with Clash Royale's soft launch on 4/1/16.
On 19/2/16, the Balance Update increased the Skeletons' hitpoints and damage by 11%.
On 18/5/16, a Balance Update increased the Skeletons' hitpoints and damage by 5%.
On 21/6/16, a Balance Update decreased the number of Skeletons spawned to 3 (from 4).
This also changed the numeral "Four" to "Three" in the description and replaced "swarm" with "surround" due to the lower number of Skeletons.
The balance changes to the Skeleton Army (in the Tournaments Update) tell us that the 4th Skeleton from this card moved to the Skeleton Army.
However, the Skeleton Army only has 16 skeletons and not 21 as of the 20/10/16 Balance Update.
On 13/2/17, a Balance Update increased the number of Skeletons spawned to 4 (from 3). This also changed the numeral "Three" to "Four" in the description.
Also with these cards, they are the only cards at max level can be killed by Crown Towers in 1 hit.
Skeletons deal the same damage as their health. Therefore, if 2 Skeletons of the same level duel, then they would kill each other in one hit. The latter is shared by the Sparky, however, Sparky deals more damage than its health.
They are the only card that is unable to do any damage to Crown Towers by themselves (unless it is many levels higher than the Crown Tower and the Crown Tower is distracted). This only applies to this skeleton card variant, though.
At Tournament Rules levels, one skeleton deals more damage to a tower per swing than the Miner.
The Skeletons and Skeleton Army have a funny relationship in that when the Skeletons were nerfed to have only 3 Skeletons from 4, the Skeleton Army received 1 Skeleton. When this change was reverted, The Skeleton Army lost 1 Skeleton, and the Skeletons gained 1 unit.