The thought echoed in the monster's head as it looked at the being in front of him with disbelief. As an A-rank monster, the Troll Overlord has its own pride, and normally would not bow down to any being.
However, the stack here is its life. If it refuses to, it's likely the spear will thrust into its eyes, killing it.
Meanwhile, Alros watched calmly. If the Troll Overlord did not agree to submit, he had to kill him. It is an unfortunate thing to do but he could not keep such a dangerous wild card with him.
He already did the same mistake before, allowing a Goblin King to enter without making it submit. The end result, deaths of several Demon Goblins and the entire Goblin King's tribe as it tried to perform an uprising.
He personally handled the execution of the Goblin King himself, and it is satisfying to watch. So, he did not plan on letting the Troll Overlord joined without submitting, as he would be able to subdue it only when it does that.
