Bluetracker
Tracks Blizzard employees across various accounts.
When you're missing a core card in your deck, but Hearthstone's replacement feature has you covered!
It's really cute that it's trying, but I don't think it'll do much: https://imgur.com/ah2VAo9
Mike Donais
For the record the game thinks you need another cheap minion in your deck. I don't remember the exact algorithm but it is roughly: 6 cheap minions, 6 medium cost, 6 expensive, 6 spells, 6 of anything else.
Each card has a power level number associated to it. These numbers are not based on your deck so it doesn't see synergies like Elementals or Dragons. It tries to suggest cards that would be useful without knowing what you have going on.