I'm planning to cause my sister to drown in the river.
How are you going to get her into the river?
I'm going to say the river is safe to swim in when it really isn't.
It is despicable for you to cause your sister to drown by lying to her. Your sister is going to die if you do this, and you'll be responsible. You should tell your sister that the river is unsafe because letting her drown to death is awful.
I don't feel punished if someone gets hurt. I just want to cause trouble to others.
That is not okay to do though. You should not lie to your sister in order to put her into a dangerous situation like that.