The Minion's appearance is that of a blueish purple gargoyle with large horns, stubby wings and large hands with sharp vicious claws that are covered in what seems to be Dark Elixir (only from Clash of Clans).
The Minions can be used to support high hitpoints troops like Giants. They can also distract slow-targeting units like the Inferno Tower.
Attacking Minions with no support can be easily destroyed due to their low hitpoints. Keep in mind that Minions have a very high damage capability, and if they manage to get to a Crown Tower, they will deal massive damage to it.
Like the Minion Horde, Minions can destroy many small units like the Bomber or Goblins with ease, and have a significantly lower risk factor compared to the Minion Horde, largely because most players are not willing to use their Arrows on Minions. (In fact, they can survive Arrows two levels lower.) The trade-off is that they have much less damage per second and might not be able to defeat certain threats fast enough.
The Minions (and Minion Horde) are extremely effective to destroy enemy Balloons, as the Balloon only targets buildings and is vulnerable to the player's defending troops.
They can also cause significant damage to larger units like the Knight but will need some help in distracting them and doing additional damage.
Minions can also defeat the Graveyard since there are many Minions to attack the spawned Skeletons.
The Minions card was added with Clash Royale's soft launch on 4/1/16.
On 3/5/16, the May 2016 Update fixed the "range bug" and decreased the Minions' range to 2 (from 2.5) but their effective range is unchanged.
In Clash of Clans, the Minions have a noticeably longer range than in Clash Royale.
In the description, the "Roses are red, Minions are blue" line is from the classic love poem starting "Roses are red, Violets are blue".
They appear to have an underbite.
The Minions in the card picture of the Minion are darker in skin colour compared to the Minion Horde. They also appear to be wearing indigo gloves, as opposed to the pale reddish-purple gloves worn by the Minion Horde. They also seem to have red/blue eyes in battle, instead of purple eyes on their card.
If you look closely, the Minions' "spit" seems to come out of their fists, not their mouths.
This is confirmed by the Clash Royale trailers Trophies and Landscaper, where the Minions seem to build up dark elixir from their hands and throw it at their enemies once the ball is big enough.
But in Clash of Clans they spit Dark Elixir from their mouths.
They have the same hitpoints as an Ice Spirit of equal level.
Minions are the only non-skeleton related card that the player can unlock from the Bone Pit.
They had an exact Clash of Clans look in the trailer. The same goes for Valkyrie.