You can get this trophy anytime after you get the blood (hematic) grenades in episode 2. Don’t waste your time with the level 0 grenade you get earlier in game they are ineffective.
*** Spoiler - click to reveal ***The crusher will appear anytime that BB senses the BTs. First let the hands in the black goo grab you, then a BT swoops down and pulls you into a rushing wave of black ooze. Immediately thereafter, the big whale/giant squid crusher will appear.
. If you can hit it in the mouth at least 3 times with the hematic grenade, you can kill it. You’ll know by his gold health bar. Happy hunting!