If the taming blow attack reduces the enemy's HP low enough without killing it, then the monster will become an ally. You just need to do controlled damage to it first and be familiar with how much damage this attack does.

Remember that you can't get champions and bosses to join this way; against them, taming blow acts solely as a damage attack.

There is a passive skill that will reduce the effect of any terrain, if the game decides to give it to you.

The only way for Shara to learn a skill from another classes is to open a Pandora's Box. If you want, you can disable Pandora's Boxes before starting a game, and then Shara will only be able to learn her own skills.

Ok thanks for clarification, I played Shara campaning about year or two ago and then on normal monster Taming blow always works. But now devs should change description of skill (at last mention about HP margin to taming).