Argo
The mana signature the demon beast gave off also had a resemblance with Eren's mana signature. The mental connection he shared with his newborn demon beast also stabilized, enabling both the beast and him to feel what the other was feeling or thinking about.
The butcher had to admit that despite all that had happened, purgatory was a huge opportunity for Eren. Maybe an epic-tier beast wasn't enough for her, but for Eren who couldn't count on his most trusted partner, this beast was a huge power-up.
Eren also understood at this point that Eliza had only offered him the beast so that he could make effective use of it when she assigned him the task she wanted to be done by hook or crook. He didn't believe for a second that the beast was offered to him out of Sage's goodwill.
After all, a gryphon could be a suitable mount for him to fly. And that enabled a more effective set of tactics he could apply to all of his plans. Tactics that were difficult to counter.