As soon as you hit Stage 18 for KC cup, have fun dueling with nothing but Sylvans. Had to tweak my Aster deck to get to Dlvl Max and it worked really well with synergy:
2x Decider
3x Drilldark
3x Celestial
1x Vyon
3x Mask change
2x Chalice
2x Divine Wrath
2x Econ
2x Cosmic Cyclone
Destiny Calling skill