Basilisk is a long range plasma cannon (LRPC). Built by all T2 land/air cons it is able to shoot targets across the map.
On most battlefields placing it on the frontline enables you to take down buildings in enemy’s base. Not very effective on mobile targets.
When built, it immediately becomes a priority target for your foes, try to keep it safe.
Can be countered with plasma deflectors, but those come at a high cost.