|Ursula's base kit served the general role of dealing with horses on Player Phase, so, with little investment, she can be used to counter the very popular horse units (except Brave Lyn), and also plenty of blue/red mages, due to her fantastic res stat.
Carrying the Blárwolf+, she has a 50% extra attack against enemy horses, which means that she will almost surely one-shot any that she engages on, barring high-res greens like Cecilia.
Her assist is the usual Reposition/Draw Back choice, even better for her because of her increased movement range, due to being a horse unit, making any other choice almost meaningless in comparison. In terms of special, Draconic Aura adds a good amount of damage to her attacks (usually more than Iceberg, while Moonbow boasts a lower cooldown.
Ursula comes with Death Blow 3, which is great for her role of taking down horse enemies on Player Phase, due to the amazing +6 attack bonus it gives, without requiring any conditions other than initiating on a target.
Her B skill should be picked to better deal with non-horse mages, since her weapon is already excellent at dealing with horses, and her res stat allows her to do much more than that. With B Tomebreaker 3, she can deny faster mages the double, and have herself double them in return, greatly improving those matchups. If she is required to deal with fast lance enemies, Lancebreaker 3 can be used to double them to death.
Her C skill choice depends on whether or not she's with another horse unit. Threaten Res 3 serves very well at reducing enemies' resistance to allow for more damage, while Hone Cavalry is better if she has a horse buffing her, allowing the two to grow much stronger together.
The seal choice depends on what opponents she usually needs to deal with. If the additional speed allows her to double crucial opponents, the speed seal should be taken, while the attack seal should be taken otherwise.