Boots of Swiftness acts as Mobis
While playing Thresh I often buy Boots of Swiftness and I always felt like I was slower at some points. Today I realized while playing that my movement speed was lowered mid combat. I repeatedly tested this, checking my movement speed out of combat, then hitting a minion and watching my movement speed going down until 4-5 seconds later. Can recreate just buying the boots and going into combat.