Help with a mod!

I am currently working on a mod and would like some assistance as I am new to this. I am trying to mod these features:

1. An aggressive mob that when spawned, will hunt the player and teleport. Can only be spawned by placing a special block.

2. Said mob will freeze players if they are touched, when players are around the mob, the screen will develop frost gradually.

Thanks, Please comment if you can help!