Heroes going for 400 Battle Points, instead of 4000.

@RudyRoared 
Yep, @Szaby59 is correct, for this weekend there's this event which allows many heroes on each side, and their costs are a lot lower then normally.

However, as it's written in @Straatford87 's message, it should be a 75% discount and 9 heroes per side, instead of 90% discount and 11 heroes per side. But that's probably an outdated version of the event's description that Tom forgot to update.