Agree with ghelas -- Baldovino is better.
How does cassendra manipulate power.... as the others have said go with Baldovino, or if you want to be sneaky use Daqun. if you are rolling on clintz use Splata Cr (i think he is slightly more useful than Baldovino)
His ability is not situational like Erpeto, and because he's a 4*, unlike Cassandra and Erpeto, you can fit in more powerful cards in your deck.
This doesn't answer your question, but in a fight, Maciej beats both Cassandra and Erpeto.
I personally think Splata is the best 5* option, dat big SOA. anyways, I find Grudj to exceed in many places others fail. hes also a 4* so thats nice, and hes a 8 power.
Have fun playing what has grown into my fav. clan in the game