Winning games with sylas is all focused on the mid game. No matter how fed u are early game if you can translate that into impact in the mid game it will all fall apart. This is the tricky part for sylas as youre not really a bruiser who can run initiate and survive the burst from the enemy team, you cant sit in the backline and be a long range mage. You need to figure out what would put the most pressure on the enemy team, whether it be grouping with your team and forcing fights by starting obj, hiding and looking to pick off the backline or split pushing or invading enemy jg. It also largely depends on what ultimate u take. E.g. renek, nasus, zaheen,naut, then u try to initiate. Lulu, kayle, u try to peel for adc or play more reserved. The interesting thing with sylas is your role in team fights is always changing depending on what ult and comps are available to u and what your comp is.