How can I acquire the Female Paladin hero of Hearthstone?

I'm a novice Hearthstone player and I have seen that there are currently three collectible heroes to buy: a warrior, a hunter and a mage.

However, when matching random games in Constructed play, I have seen players that have another hero that is not in the shop list, a female Paladin.

I really love that character, so I investigated and discovered that the way to acquire that Hero is by joining WOW game and leveling up a character to level 20 (a paid account is not needed to do it from what I have seen.)

Please now let me ask some questions which are closely related to each other to help me understand this:

1. At this precise time, on 29/June/2016, am I still able to join WOW to acquire the female Paladin reward?. (it seems that it had a time limit that ended in March, but I'm not sure.)

2. Are there more heroes that are not in the shop list and require special actions to acquire them?. (please, give full hero names or links with further documentation.)

Solution 1:

1. You actually receive the Paladin Hero through an ingame 'Feat of Strength' achievement, which should still be accessible - achievements doesn't usually disappear, especially Feat of Strengths, unlike WoW 'events'. For what it's worth, I recently leveled with a group of friends, and one of them got it!

2. There's also another Mage hero, Khadgar, which is no longer accessible. According to the Hearthstone gamepedia, he MAY become accessible again in the future, but I haven't personally seen any real source for this.

Solution 2:

1. Despite the claimed time limit, Lady Liadrin seems to be still available as of June 29th.
2. Sadly, yes, there was Khadgar, the third mage. He was exclusively available for purchase for iOS devices as part of a promotion campaign "Apps for Earth", which persisted from April 14th, 2016 to April 24th. (Although the campaign was available only for iOS, once one bought him, then they could use him on any device linked with the account, even on Android.)