Risen Executioner’s last ability doesn’t change when you can cast it.
2015-02-25
Once you start to cast Risen Executioner from your graveyard, you’ll finish casting it, including paying its cost, before any player receives priority. No one can respond in time to affect the cost you’ll pay (perhaps by destroying one of your other creatures).
This creature can't block.
Other Zombie creatures you control get +1/+1.
You may cast this creature from your graveyard if you pay more to cast it for each other creature card in your graveyard.
more to cast it for each other creature card in your graveyard.