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Sad DJ
Napstablook is a very good card when it comes to initial damage early/mid game. Although its ability may make Napstablook seem useless, its high stats for its price make up for this downside.
Combos
Using silence on Napstablook via the Nacarat Jester is a good way to remove the attack loss of this card (and bring its ATK back to 5). Particularly useful in Bravery by using Strength to give it more ATK, or you can use Snowdrake if you aren't playing Bravery.
Counters
By using Faun against this to make it have 2 ATK can be very bad for you. Also using Ugly Fish against this to lower its ATK.