205.1b Some effects change an objects card type, supertype, or subtype but specify that the object retains a prior card type, supertype, or subtype
The Seriema doesnt turn into a creature until you manage to Station 7 power worth of creatures into it
It's not the most useful tool during the first few weeks of a format, but it's excellent for formats that have existed on Arena long enough for the site to gather larger sample sizes of player data.
Just note that all of your tokens created with replacement effects will enter tapped, just like the original
Ward for three life on a 3-mana 3/3 with menace and lifelink is really good on a generic creature
Oath of the Gatewatch and Battlebond have since normalized this kind of rules language, and this card looks like it would slot in perfectly as part of blacks limited, but powerful, suite of mana rituals