Legality of using trademarked words in game name.

I am a newbie to this forum. I hope you will all forgive any potentially naive / obvious questions I may ask.

I have developed several games which are basically add-ons for another fully copyrighted, trademarked games. They would require posession of the original game to be useful. They would not include any licensed wording or designs or pieces from the original games. However, I am worried about two things that I hope you all can shed some light on.

1) Is it legal for me to design a game whose soul purpose is to be used as an add-on for another game owned by somebody else or, do I need to receive permission from the company in question to do this?

2) Is it legal for me to use a trademarked name in the name of my game if I give proper credit to the owner of the trademark?

An example would be: I develop additional rules for Uno, and sell the rules, along with required dice, and special event cards. I then call the game "Power Uno", giving credit to the makers of Uno for the trademarked name.

I have already verified the trademarks through uspto.gov, and have sent emails to one of the companies involved (Hasbro) receiving a form letter in reply with no relevent content. I was hoping some of you might have good advice for me before I go down the long road of testing and production, only to find out I cannot sell my creation.

Thanks in advance for your help.

--Doug