Well whatever it is, creating new money and giving it to someone increases their purchasing power compared to what it was previously, which all other things being equal means a reduction in everyone else's purchasing power.

That depends entirely on how much excess capacity there is, it's not per se inflationary. If you mobilize idle capacity with new money, then you're increasing the size of the pie (more money chasing after more goods).

That's why I said "all other things being equal". In the general case is which there's no excess capacity, which can be assumed if the economy isn't undergoing a recession or the like, it's inflationary.

It doesn't even have to be recession. Slow growth and high unemployment (such as what we're seeing right now) also indicate that there's plenty of room to mobilize idle capacity.