Minions in the Hand can be affected by targetted Battlecries, Spells and Mirror Entity and use their Battlecries about hs-bugs

[Xinhuan]

If a minion is Enraged by an effect/spell while it is in the hand, the client of the player with the minion hangs and has to reconnect. After reconnecting, if that minion with Enrage is played, the opponent hangs and has to reconnect.

https://www.youtube.com/watch?v=HgaX8I016u8
Testing by culinko and PattuX.

Video description as follows:

Testing under which circumstances players hang when a minion is damaged in hand.

It turns out it probably happens with every Enrage minion (tested Amani Berserker, Raging Worgen and Spiteful Smith), no matter whether it was enraged on board or not. The player with the enraged minion hangs as soon as the spell hits and has to reconnect in order to continue playing. When he plays the enraged minion targeted earlier, the player casting the spell hangs and has to reconnect in order to continue playing.

The Enrage minion that is damaged in the hand does not have its Enrage effect trigger - it does not gain attack, or Windfury, or buff your weapon (Spiteful Smith).
Logs: https://gist.github.com/culinko/ece6aa9e27a6e252af9e

This does not happen with other minions, including ones with Deathrattle (tested Mechanical Yeti and Cairne Bloodhoof) and On-Damage triggers (tested Imp Gang Boss, Mech-Bear-Cat and Wrathguard). They are displayed as damaged in the hand, possibly with negative health but their health gets reset on playing. Their deathrattle/on-damage trigger does not go off.
Logs (Swipe on Mech-Bear-Cat): https://gist.github.com/culinko/db80954a1c58ff0f8fac

In addition, using Mortal Coil on a minion that is reduced to 0 health in the hand draws a card but does not kill/discard the minion.
Logs: https://gist.github.com/culinko/2295a0b2373b42e946b0

[culinko]

If you use Gang Up on a minion in hand, the 3 copies going into the deck will form around the card in hand, invisible to your opponent.

• https://www.youtube.com/watch?v=MqZEzkyb95M

[Patashu]

bumping to 5.2.0 because it's pretty clear this stuff still happens as is.

spun the enrage hang into its own issue because it can be fixed independently: #579

[culinko]

There is also at least one client side hang - if you transform a minion in your own hand, your opponent's client will hang, and they must reconnect to continue playing. (This is shown in Wrong Zone Battlecries and Spells # 1)

Reproduced the hang in 7.1.1.17994 with a friend.

[culinko]

Mirror Entity still copies a minion that has been bounced to hand before the Secret Activation Phase starts (tested in Patch 8.2.0.19506).