Other Elementals you control get +1/+0.
{2}{R}{G}: Creeping Trailblazer gets +1/+1 until end of turn for each Elemental you control.
Because Creeping Trailblazer is itself an Elemental, its last ability will usually give it at least +1/+1.
The size of the bonus is determined as Creeping Trailblazer’s last ability begins to resolve; it won’t change later in the turn if the number of Elementals you control changes.