My mars rules the 7th but it is placed in the 8th and retrograde. does it still follow that my partner is going to be powerfull?
Discussion
I'll be blunt. A powerful partner, can mean your partner can have power over you. This can be bad, or it can be good if s/he will help you and guide you in a beneficial way for you. Look to the rest of your chart. Mars can be a malefic planet, and it being retrograde in your chart indicates problems.
Clean your soul and chakras, do detaching to remove any malefic people from past lives who might re-enter your life. Focus on this for a while, and then do a magickal working to bring a beneficial partner into your life. When you do get a partner, you can do another working at some point to ensure a happy and harmonious relationship.
The placement might be fine, as it (7th house ruler in the 8th) can also indicate a soul-mate relationship with a healthy sex life.