This question occurred to me after reading this question.
That question questions if the echo can make ability checks. Given the fact that a grapple is an attack, which the rules permit the echo to do, and an opposed skill check between the creature being grappled and the knight (not the echo), the question is what happens when the grapple is successful?
The rule for the grappled condition states that:
The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell.
The problem is that the echo knight is never moved away by an effect because it was never within reach to begin with. The rules say the attack “originates from (your space or) the echo’s space. That’s not the same thing as being within reach.
Or is it? The rules for Manifest echo effectively grant the knight reach from that space because the knight can make attacks of opportunity from the echo’s space.
So what happens after an echo knight successfully grapples a target that is within reach from the echo’s space but not from the knight’s?