Yone vs Sion Top Matchup
Yone Top wins 52.5% of 2,444 Low Elo games against Sion Top, +2.3 points vs expected, 2-patch window 26.19-26.20.
Researched on LoL patch 26.20. Tips are written to hold at any rank; stats come from Low Elo ranked games up to patch 26.20.
Why Yone is favored
Yone's mixed physical and magic damage keeps Sion from shutting him down with armor alone, and Soul Unbound(E) gives Yone a way to leave Sion's charged Q or re-enter on his own terms. A high-level Sion discussion describes Yone as a difficult matchup once his damage comes online.
Measured in High Elo: Yone wins 4.0pp more often than expected over 1,029 games.
How to play as Yone
Use Soul Unbound(E) to leave Sion's charged Q line, then return to trade once the knockup threat has passed.
Way of the Hunter(P) adds magic damage to every second attack, so Sion cannot answer all of Yone's sustained damage by stacking armor.
Soul Unbound(E) gives Yone a repositioning window against Decimating Smash(Q), which requires Sion to charge before releasing its knockup.
How to play as Sion
Hold Decimating Smash(Q) for when Yone has spent E or has committed into your range; a predictable charge gives him time to leave.
Sources
These notes come from r/DirtySionMains, checked against the champions' abilities.