Spell towers such as offensive Invisibility Towers can be a useful strategy in Clash of Clans. But, they may be more complicated than you realize. I will share some videos to help with this below. Poison towers are often used to discourage and weaken blimps with Super Archers or Super Goblins.
The first video on the Invisibility Spell towers comes from Judo Sloth. It covers the basics. He covers topics such as how to trigger the tower and how not to. It also features some cautions on what not to do with it.
The video below comes from RH Base Building. This video that shows offensive and defensive uses. It shows the range of the invisibility spell. The range for this spell changes depending on the size of the building it is protecting. It also goes into what will trigger the trap and what will not trigger the invisibility trap.
The next video shows some important aspects of the Rage Spell of your Clash of Clans Bases.
The following video is also from RH Base Building and features the poison spell. This expert refers to the poison spell as the most powerful spell. It can help deter someone from flying a blimp to your TH and dropping Super Goblins or Super Archers directly on it.