FormRecycler is a Google Forms Add-on that allows you to recycle information from Forms you already have created. There is an annual subscription needed to create Unlimited questions, you can create 30 questions for free per week.

Merge Forms allows you to have multiple Forms merged into the current Form with 1 click. Just click on FormRecycler in the Add-on menu and choose Merge Forms. You can then select as many Forms as you like to merge all the questions into the current Form. 

Recycle Form questions allows you to choose one question (or many) to copy from a Google Form in your Drive to the current Form. Just click on FormRecycler in the Add-on menu and choose the Form you want to copy the questions from in the popup window. You can select as many questions as you want and even choose to 'Select all questions' at the top. (Google recreated this functionality natively in Forms in July 2019). The only pro for continuing to use FormRecycler is you can see all of the information in the questions before selecting them. Google only shows a small bit of the question information. Google does natively import the embedded images and correct answers for short answer questions (FormRecycler can't as Google doesn't expose that information for use by developers).

FormRecycler will recycle almost all question types and will be able to recycle the feedback from the original Form as well.  

Some great use cases:

Now you can use the FormRecycler Chrome Extension to insert embedded images from recycled questions! (Currently not working with the recent Forms update)