This deck is a variant to Fatzoidd's "SYLVANS ARE BROKEN?" deck.
I love Sylvans. It was one of my first two decks I went for on MD with Eldlich, because I also love zombies. They were strong enough in season 1 to get me to gold but that is where Eldlich had to take over. With Rikka support, this deck can evolve into a field clearing XYZ powerhouse.
I run 2 Rikka Petal and 3 Lonefire Blossom for consistency. Once both Petals are in the GY, you can only use one per turn, so if you want to remove one, you can, but between these 5 cards, it makes for a very easy time getting your first petal on the field/GY to go into Snowdrop The Rikka Fairy. A lot of this deck revolves around Snowdrop. Snowdrop will allow you to mimic a cards level and change all cards on your field to that level.
Foolish Burial is amazing here. It is an extra way to get Petal into the GY if you don't draw Petal, Lonfire, or Snowdrop. If you don't need to get to Petal, it can be used to mill out Spore, Carrotweight, or Rose Lover. Carrotweight is best milled when you already have Spore or Rose in hand. This lets you get a free level 4 on the field and gives you a resource in the GY to summon from hand or set up for XYZ summon with Spore. Carrotweight can be brought down to a single copy in favor of Ash, Fengli, or Called by the Grave.
Sekka's Light x2 is something I am still playing with, but it is a strong card and not very punishing if you need to use it. Between the two copies, you can draw 4 cards and re draw 2. Try to save them for after you have used Foolish and Miracle Fertilizer if you can, but this is not necessary if you need the draw 2. These can also be swapped for Called by Grave, Miracle, or Ash.
Miracle is really strong with XYZ as well. It beats out Monster Reborn because it can special summon across multiple turns. It consumes your normal summon, but this isn't an issue. It's true power comes from summoning XYZ material. It reads, "If a monster Special Summoned by this effect leaves the field, destroy this card;" however, if you use that special summoned monster as XYZ material, it never left the field and it is no longer special summoned by Miracle, so detaching to GY does not destroy it.
Rose Archer is a bit of more fluid in this deck, but I run it because it works really well with plants and it is a very budget card. Alternatively, you can run Ash, Effect Veiler, Maxx "C", Ogre, or Imperm. Archer is also a great hand trap to combat the Imperms.
Evil Thorn could be worked out for something else, but it makes an easy way to summon Princessprite. Turn one with Petal can search Snowdrop, tribute Petal, summon Snowdrop and Thorn, then activate Thorn and summon the other two from the deck. Use Snowdrop to set their levels to 8 and summon Teardrop the Rikka Queen off of the Thorns leaving Snowdrop in def.
Using the first part of Snowdrop locks you into plant special summons, but if it survives, next turn you can set another monster to 8 and XYZ Number 97 and XYZ 97 into Number 92 if needed. Otherwise Number 107 and Hieratic are strong non-plant options. Just remember that if there are no plants on the field, Rose Archer is useless.
Dark Armed, The Dragon of Annihilation is currently in the deck, but it doesn't see much play and could be swapped for something else. It is a little tricky to get out as it requires at least 1 Dark XYZ to be in GY and then Snowdrop another dark monster to level 5+, but it creates a strong 1 cost XYZ. Alternatively, Number 87 is a strong base attack with ok effects option but has a high cost of 3 level 8 monsters. There is also Sacred Tree Beast which has a strong effect, but cost 2 level 9 monsters. This requires to Spore off one of the 4 level 8's in the deck and isn't the easiest summon, but sets up a great negate and has easy material generation.
Other Side Deck options are there as some decent swaps to the more flexible cards in the deck. If you want to run 3 Ash, I would personally take out 1 Cherubsprout, Carrotweight, and either a Gaurdioak or Miracle. Play around and let me know what you think!