In other words, WordPress plugins are almighty. Consequently, any WordPress plugins can get your website penalized. They can hide content from Googlebot without you being aware of it. For instance, GoogleBot may not be able to see images and text because of a plugin.
They can add hidden links on your web pages. The links can be in a form, at the bottom of your web pages.
They can block access to some of your webpages thanks to googlebot or by adding a robot meta tag to your webpages, a directive to your robots.txt or even a X-Robots-Tag to http headers. Check this page from google about it.
Also, they may slow down the page load of some pages without you being aware of it.