Here's the Scenario. I want to be able to summon a will-o--wisp for however long I want. Then be able to cast the spell again and make him go away. Except I want this wisp to be super powerful, like anyone gets close, 1 hit death. How would I make a mod like this?

Basic Scripting : http://cs.elderscrolls.com/constwiki/index.php/Scripting_Tutorial:_Basic_Scripting_Knowledge
First Spell Tutorial : http://cs.elderscrolls.com/constwiki/index.php/Scripting_Tutorial:_My_First_Spell
Summoned Creature Tutorial : http://cs.elderscrolls.com/constwiki/index.php/Scripting_Tutorial:_Summoned_Creatures

Between these three, you should have enough information to be able to make the Summon-- then you can just alter the creature's Attack Stats