I usually run x2 Marsh Song coupled with the new jelly's ability. Most of the time in my meta/collective bg I have 3 marsh songs active. The 30 nora per turn is nice.
Creativity I believe is what it is called. Every time he attacks all your non-champ runes get -1 on their CD
Marsh Song helps ease the costs of other spells like PHS, Reverb, Backfire Boon/Backfire and Font Erupt and combined with Creativity like Rosch mentioned can allow u to liberally use aforementioned spells while still being able to deploy consistently. MS gives FS more late game potential. I just fall victim to 30 rune slots and liking many runes so i can never fit multiple Marsh Songs in a deck without leaving out things ill miss in game.