Hearthpwn

This is a 3/10, too hard to play in Handlock without damaging your own giants, even worse in zoo. Zoolock? Nope. Unless you run 80 % Mechs, this is terrible. Especially since Warlocks use Demons a lot.

I just realized that this actually has anti synergy with mortal coil while Demolisher has better synergy in comparison due to the fact that you will not be able to draw a card from a 3 health minion on the board.

Anti synergy? Mortal Coil can snipe something that has 1 health to ensure Cannon hits for two damage. Besides, happening at the end of your turn makes Fel Cannon much more reliable in the first place:

Imagine how much Ragnaros would lose popularity if it  at the start of your turn.

Fel Cannon seems a worseDemolisher in some conditions and better in others.

But we can run the two on the same mech deck :D

Strong body, good counter to deathrattles that summon minions 

it deals 2 dmg to a non-mech minion, so you don't want them to have a mech deck

Not really excited about warlock mech decks, was hoping for much more demons in the play.

As soon as people start playing mech decks less this card will be in most of the warlock mech decks.

Basically this card will be stronger now in a mech deck as many people will not have mechs yet and it will become weak(er) in a while when more people have mechs and then it will be average. Just my personal opinion though.

It seems a lot stronger than Demolisher as it deals the damage at the end of the turn and not the start of your next turn.

Theoretical situation: Turn 6: Nerubian Egg and this card-> turn 7: If this card did not hit the egg then you void terror the egg and this thing together otherwise you can just terror this and then play another 4 mana card. (Ofc this is is highly situational)

It has anti-synergy with Flame Imp and maybe it can cause a midrange/spell/mech hybrid orientated warlock deck to be viable: Nerubian egg, Void terror, fel cannon, spells and whatever else works well.

This card immediately dispatches a fresh Shade of Naxx before it can get its buff, trades favorably with yeti, and can clean up quite well against the low-health minions in an aggro deck. Seems like a great card to me. It is annoying that you cannot guarantee an enemy minion is hit, but if they let you target the minion people would complain that the card is overpowered. You can't have it all. Set up a scenario in which the card will most likely work out in your favor and it will most likely be fine. You don't need an entire mech deck to ensure it NEVER hits any your minions EVER in the history of time. That's silly. Just play the damn game.

This card doesn't  say "random". Hope one can choose the target.

Only plays you make during your turn let you choose a target (battle cries, spells, hero abilities). All other effects not due to plays you make directly are random unless stated otherwise.

Please correct me if I am wrong or if there are cases that work differently.

Is it supposed to counter the players that refuse to use the new mech cards?

Yes, at the cost of constraining yourself to 100% mech and playing warlock. Also consider that 2 damage to a random minion isn't the significant for most control decks which are happy to sit minion-less, or at least play tougher minions that can shrug off 2 damage.

An interesting thing to note that makes this card better is that the effect is end of turn not beginning so as long as your opponent has a non-mech minion on the board you will get instant value as opposed to demolisher which is beginning of turn.....only problem is that it makes it risky to drop a non-mech minion on your side of the board because the effect can hit your own minions.

Compare Fel Cannon to Demolisher.  Costs 1 more mana, get 2 more attack, 1 more health, but can only hit non-mechs.  Meh doesn't seem good to me.

Nice card, hopefully we'll get to see a new archetype for warlock.

Not sure if it is good card for warlock