It costs 8 at base.
The AirElemental has the ability to upgrade itself by using its Magic [Ranged] on an enemy unit. At +++, it instead summons sylphs. This ability makes the Magic targeted areas important to avoid, unless you want to. However, it loses value on kill, and if its value reaches 0, it dies, forcing you to use its magic to avoid losing the AirElemental.
Quick Stat: AirElemental Edit
|Tier 1||Tier 2||Tier 3||Tier 4|
Tier 2: AirElemental+ Edit
Changes from AirElemental: 2
Tier 3: AirElemental++ Edit
Changes from AirElemental+: 2
Tier 4: AirElemental+++ Edit
Changes from AirElemental++: 2
Airelemental is able to use its ranged magic to have control over an area, as an opponent will not want airelemental to promote or gain value. It also gains more and more orthogonal control as it upgrades, causing it to be more dangerous and almost like a more powerful rook. Airelemental also is relatively cheap at lower levels, allowing easy trades even if it dies in the process.
Airelemental can only take two pieces before it dies, unless it promotes. In addition, if its magic is blocked by pieces, it cannot push them. Finally, at +++ it can get only 2 kills. The sylphs can also be counter intuitive if an opponent has a vampire or pride.