Aloy can hack Machine Beasts by using her unique spear to get their help. For example, Broadhead carries you wherever you go, Watcher fights against machines together with you, and Tallneck provides you area information and make the system of machines around you down temporarily.
Tips
To safely override fierce machines, you need to get close enough to use the spear stealthily.
Tallneck has a connector at the top of his head, so you have to climb up his neck to hack it.
