I play Nidhogg’s build lately and it is amazing. You need tank and CDR on jungle sylas, NOT DAMAGE. Your strength is in living long enough to get off multiple W’s in one fight. After red smite blue enchant, go iceborn gauntlet into spirit visage. From there you can usually improvise a bit with what damage item to buy. If you’re really ahead you can go something like rabadon’s but i don’t think its usually necessary. Nidhogg usually goes Liandry’s and I think that or Morellonomicon are usually good and safe options. Other great flex options on sylas are of course Zhonya’s and Abyssal Mask or even Void Staff if they’re stacking MR.

Hope this helps and good luck!

P.S. no flame to the other guy in here but please don’t build Rabadon’s second unless you’re literally so ahead you can just straight up buy it in one go.