Another crucial champion. While not as mandatory as Knight of Seasons, if Ursa doesn't show up in your opening hand, you should try to play; it as it's a good source of damage.
Ursa is tricky to use. If drawn midgame, it lets you burn cards aggressively, knowing you can spend your magic on multiple Ursa summons.
Its main value is attacking and then hibernating back into your deck. But timing this is not easy. Ideally, you want it to absorb damage before it hibernates, but surviving is easier said than done. Smart positioning, Guards, and Shroud of Autumn help make it work.
Ursa takes thought, but offers massive value if played correctly.