Both the top two abilities look very low powered. "Tap target permanent" isn't very useful at sorcery speed. I note that both Ajani Vengeant and Tamiyo, the Moon Sage have gone for the "it doesn't untap during its controller's next untap step" approach. That's the kind of +1 I might expect to only see on a two- or three-mana walker. The -2 is kinda interesting: at sorcery speed it's somewhat similar to "Tap target permanent" in that it neutralises a blocker for a turn. Obviously it can be used on your own ETB creatures too; that mode was most iconically used on Venser, the Sojourner - but for him it was +2!

The flavour intrigues me somewhat. The name sounds like an allusion to Sorin Markov, but the mechanics seem to suggest a very white weenie aggressive strategy, and it's a little hard to imagine a vampire leading that kind of strategy...

Changed the +1 to +2 so it's weak but charges up quickly and the -2 to -1 so its a bit more useful.
Considered having him a but wanted his cost to "match up" with the two classic inspirations for his ultimate Wrath of God (actual cost)and Armageddon (same cmc).

Name had nothing to do with Sorin, Its a bit of a preview for one of my other sets that I am working on offline that is heavily influenced by russian/baltic folklore.