"He is a wonderful partner."
Translation:On jest wspaniałym partnerem.
in the sentence "he is noun" you use on jest + noun (instrumental), if an adjective describes the noun it has to agree with it in case,number and gender.
Singular masculine instrumental of wspaniały - wspaniałym
I have a slight suspicion that Ellikin could have "why there are five consonants in a row?" in mind.
"wyspanle" doesn't really look like any word that I know. You mean "wspaniałym", probably - and that's the main answer.