Calling it now: Rek'Sai will be OP top lane upon release
Only because of the passive
"Activating Burrow with Fury will grant Fury of the Xer'Sai for 5 seconds, which causes Rek'Sai's next source of Fury generation to grant 15 bonus Fury and, so long as she remains burrowed, to expend 20% of her current Fury every second to restore health. The health restored is based on the amount of Fury expended, for a maximum of (25 × level) health over 5 seconds if she burrowed at 100 Fury."
Thats a ridiculous amount of healing on basically no CD at all
Burrow is on a 4 second CD after burrowing btw