This is the 16390th most frequent Polish word.
walentynkowego
"Of Valentine's (Day)" or "Valentine's-related."
Here, 'walentynkowego' is used as an adjective describing the teddy bear, indicating that it is associated with Valentine's Day.
Dostałem walentynkowego misia od przyjaciół.
I received a Valentine's teddy bear from friends.
In this case, 'walentynkowego' modifies 'nastroju' (mood), showing its attribution to Valentine's Day celebratory atmosphere.
Walentynkowego nastroju nie można przegapić.
One cannot miss the Valentine's mood.
Here, 'walentynkowego' qualifies 'wieczoru' (evening), marking it as related to Valentine's Day occasions.