Hello everyone again.
There's some creatures what just take anotherone with them when they spawn.
Examples:
Wintergasp siege engine always spawn with a
Wintergasp siege turret attached. Same situation goes on with the
Hover Disk wich always spawns with a
Scion of Eternity mounted on him.
Now, the question is: how these creatures works? how can I made by myself a creture who spawns another creature attached or mounted on him?