The target needs to be near the Rex, not your model. Also, why would you be giving crows to the one model in the crew that already has built in crows?
You use tendrils when you need to move something/get a third attack if you're holding a high ram, and you use wild hunt to set up for Titania+whoever else is there.
It's a good meme. Rex with Inhuman Reflexes and access to all the abilities from Marcus' upgrades is super solid.
True, but it is terrifying 12 in a keyword not known for terrifying, with access to injured in keyword, has 12 health, a way to self heal, HtW, as well as Titania making it immune to RJ damage flips. It's job is to just be in the thick of things with Titania, empowering her main attack and also forcing your opponent to either try and focus down the Rex and leave Titania alone, or focus down Titania and leave the Rex alone.