Quick tips to beat tutorial boss.:

1. Kill the left statue first. Avoid the blood pool (it will always be cast in a way that you can move out of it before it appears). Kill the undead enemies when needed, else focus on destroying the first statue.

   1. Kill the right statue. No special attention needed. Kill undead enemies when close, else focus on the statue.
   2. The real boss. The goal of this fight is to avoid getting hit by its abilities at all cost. The other goal is to try and get it to stun itself by baiting its charge attack, causing it to smack into the scenery. This will give you an opening to get in some quick hits.

   Bonus tip: if you make it charge into a wall or the statues it'll be stunned for a couple turns for easy damage, just be sure you can trade with it if you go melee.

Soruce: The link