Sion vs Teemo Top Matchup
Sion Top wins 54.0% of 2,146 Low Elo games against Teemo Top, +3.7 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 Sion is favored
Roar of the Slayer(E) can slow and reduce Teemo's armor from range, setting up Decimating Smash(Q) and Soul Furnace(W) while Teemo is trying to retreat. That ability sequence lets Sion punish Teemo through his ranged poke and blind, which only interferes with basic attacks.
How to play as Sion
Use Roar of the Slayer(E) through a minion to slow Teemo, then charge Decimating Smash(Q) and pop Soul Furnace(W) while he tries to escape the combo.
Roar of the Slayer(E) can slow and reduce Teemo's armor, and the slow can make it easier for Sion to land a charged Decimating Smash(Q).
Soul Furnace(W) adds a shield and nearby burst to the E-to-Q combo, so Teemo cannot stop Sion's ability damage by blinding him.
How to play as Teemo
Use Move Quick(W) to sidestep Roar of the Slayer(E) and avoid letting Sion chain it into a charged Decimating Smash(Q); disengage instead of trying to trade through the full combo.
Sources
These notes come from r/topmains, checked against the champions' abilities.