Vex & Amumu Reroll

We are playing an early game around the Superfan and Annie Headliner traits, we want to roll to level 6 to get a better Headliner such as Seraphne and then reach level seven to hit Vex, it is worth playing on someone else's items temporarily because Vex 2 without Chosen is very weak. As a second carry, we can play Poppy under Bruiser Items and we put tank items in Amumu, which we also make for 3 stars when making Vex, it gives a huge power spike in the mid-game if we hit it quickly.