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It's still not clear what this means. A withdrawer captures by making a move, whilst an immobiliser stops others from making moves — the former's effect is on its own turn while the latter's is on the opponent's.

As such there's a couple of interpretations possible:

• It stops things from moving away like a withdrawer. This is just a weaker immobiliser, and is already attested in Euqorab
• It petrifies pieces that it moves away from rather than capturing them. Then the question is whether and if so when pieces can come back into play: never (as with Nemoroth's basilisk)? When the withdrawing‐petrifier moves again (leaving it able to only petrify one piece at a time)? After a larger but still fixed number of moves (turn counting, ugh)? Under some other condition? Are involuntary moves (from Swappers, shepherding pieces, Go Away!s, ⁊c.) counted? Does capturing it release pieces?

Imo the former option is not very interesting, nor necessarily well‐defined (how does it deal with knights?), while the latter is quite complex in principle and perhaps not very immobiliser‐like — though I admit the possibility of ulima‐style pieces with effects besides capture is interesting and not very well explored