Hearthpwn

 

Illuminate is a 3 mana tempo gain with a discover attached, how more broken does it need to be? If we're talking about cards in a vacuum I don't think you can get much stronger in power level. It will have full effect with any spell costing 3 or more, in any deck, in any class.

A three mana tempo gain (maybe) next turn at the cost of 1 card (in a vacuum) and doing nothing now.  I only play standard and this card see's very little play.  Maybe it's abused in wild in combo with other things, but not in a vacuum.

Whether it's the strongest card or not is impossible to say (philosophically - what does that even mean?  Best played win rate?  Best mulligan rate?).  That said it's definitely too powerful for it's mana cost (imo) and the fact that locations are essentially unable to be stopped makes it feel rubbish to play against. 

Blizz has shown a tendancy to make cards with a strong upside in exhange for a downside.  This works in theory, but in practice it doesn't work because it's impossible to balance,

1) If you make the upside so large it vastly overcomes the limitation, then many decks play it for the highroll potential (Zephrys for example - played in several non-highlander decks). 

2) If you make the limitation too small (e.g. in this case play some imps) then all you've done is print an OP card (this is the situation for Vile Library imo) and was also the problem for "all spell" mage decks and elemental shaman.  There was no real deck limitation but the upside for the conditional cards was huge. It was also one of the reasons why I think quest warlock felt super shitty to play against.  Those OP cards balanced with a downside, but with the quest the downside was an upside.

3) You make the limitation too great or the benefit too small - no one plays the card.  There have been plenty "if you have XXX then do yyy" cards that just don't work.  Beast hunter cards spring to mind. Too hard to fullfill the conditions with limited pay-off.

I can see why they print them though - they're thematic and encourage a "style" of deck (imps, elementals, beasts etc.) but they really need to playtest them in the context of card set they're released amongst.