Tiberius can be damage immune during the whirling blade part of his ult. Use someone like Io or Ash, people who can cc him off the map. He can't use another move until he lands in his whirling blade stance, so he'll fall to his death.

Terminus siphon annoying you? You can ult him, which gets rid of his siphon and have your team burst him from there. Your gourd is on the ground, which damages him even if he has his siphon up.

Set out Luna, and mark Maeve so Luna can rush and stun her. Even with the stun gone, keep her marked because Luna can still deal auto-aim attacks to Maeve. Though once your fox is dead, run away. LUNA counters Maeve, not you.

Tiberius has no damage fall off, meaning 650 damage every .7 seconds and .49 seconds no matter what range you're at. The best counter is someone like eminence Lian or a sniper who can deal more damage than Tiberius from afar.