Thea the Tomb Angel is a Force legendary from the Knight Revenant faction. Thea was added alongside patch 3.0 and is one of the legendary rewards for collection the fragments from the Doom Tower hard secret rooms! She has a really fun looking kit and is the first champion to have a Hex debuff which boosts her following hits.
I believe she will be difficult to set up for maximum damage, the best option would be in ally attack teams to spread the hex before she gets her turn.
Her low base speed may make Thea a tough champion to make the most out of, but a slow nuker is likely to be the best option.