Primape GE

[nnaann]

Its whump attack says to flip a coin, if heads the defending pokemon cannot attack next turn. What if they knock out my pokemon? Do I bring out a new pokemon from my bench before the coin flip?

 

[bulbasnore]

as per this ruling, the effects all happen before the replacement, so the new active isn't prevented from attacking:

Q. If Gastly (Fossil) uses Lick and Knocks Out the other Pokémon, does your opponent bring out another Pokémon and then you do the status effect?
A. No, a Pokémon is SLATED to be removed when it has sufficient damage assigned to it. Attack effects resolve BEFORE a replacement Pokémon is brought up. (Aug 31, 2000 WotC Chat Q232)