
I'm a huge fan of Dario.
Any card that gives you a permanent stat boost is worth looking at. Dario gives you two. Incredible! Also, his ability is sort of a Cache-on-a-stick, improving any free action you might have. Undoubtedly very powerful. But he comes with some downsides.
First, as an Ally, his slot is incredibly competitive. He costs is relatively high, his soak isn't amazing, and his stat-boosting ability is tricky to turn on. But, all of these can be mitigated. If you build around him, he's great:
- Money. He costs 4 to play, which is high, and then expects you to have enough money to turn on his ability. However, any card that gives you cash to turn on his ability also gives you cash to play him. He himself gives you cash with his ability. So once you throw in a Lone Wolf or a Hot Streak(4) (or a Hot Streak(2)), he is pretty viable.
- Slots. He competes directly with Leo, of course, but I'm not convinced Leo is always the strongest option. Leo gives you actions but sucks your tempo to the tune of 6 resources. What if you'd like to bounce back pretty quickly? Dario can take 2 actions to play at a net cost of 2 resources, then can give you another 2 next turn to get set up. Regardless, if you'd like to mitigate the slot cost of Dario, Charisma is the obvious answer.
I've played him in a pay-to-win solo Jenny before to great effect. She could afford to win through Streetwise and still keep her Dario bonus up. I've also enjoyed him in solo Jim (with Lone Wolf for money), stacking with St. Hubert's Key to have a very imposing 6 5 3 2 statline. He is much easier to play around than David Renfield as far as econ options go, and he gives you as well.
So give him a try, particularly in solo decks (where 2 stats is massive)!