When you have the Symbiote Surge ability, which you get as part of the main story, you press  +  to activate it. It's basically a kind of powered-up rage mode. Once in this state, you can then use your Symbiote Abilities, which you do by holding  and then any of the face buttons . A good tip to unlock this trophy is to upgrade your focus, because you unlock your Symbiote Abilities in combat by dodging and parrying perfectly. Your Symbiote Surge also increases the speed at which these Abilities cooldown. Get yourself into a big fight (maybe a Hunter Base, see Seek and Destroy ), and get Symbiotic!