An action hit someone and changed them into a new state, and you want to name the state they ended up as, not only that it hit.
序 · The move
1put the one who takes the action first, as the subjectis this the one the action lands on, not the one doing it?
2被, then the agent if you name one, then the verbagent (if any) sits between 被 and the verb, never after it?
3attach 成 directly behind the verbnothing sits between the verb and 成?
4name the state the subject was turned intois this a new thing the subject became, not a degree of how far the action carried?
例 · Examples
1他被passive marker — he takes the action人someone (the agent, between 被 and the verb)打hit, beat (the verb that lands)成into — welds the verb to the state turned into重傷serious injury (what he was turned into)。
He was beaten by someone into serious injury.
界 · Boundary
被…V得…
被…V得… opens onto how far the action carried, a spilled-out degree (他被打得站不起來 = beaten so far he can't stand). 被…V成… names the new state he was turned into (他被打成重傷 = beaten into serious injury). 得 rates the reach; 成 fixes the end-thing.
被+（N）+V
Plain 被+V reports that the action landed (他被打了 = he got beaten). 被…V成… adds what the beating turned him into (他被打成重傷 = beaten into serious injury). One names the event, the other names the transformed result.
把…V成…
把…V成… is the active disposal: the subject acts on a definite object and turns it into something (他把書翻成英文 = he translated the book into English). 被…V成… is the passive flip: the subject is the one turned into something. Same V成 weld; subject does the turning vs. subject is the one turned.
no 成, state welded bare onto the verb: 他被人打重傷 → 他被人打成重傷
agent after the verb: 他被打人成重傷 → 他被人打成重傷
subject is the doer: 人被他打成重傷 → 他被人打成重傷 (the one who takes it is the subject)
English fuses passive and transformed state into one clause ('was beaten into a coma') with no separate marker on the verb; learners drop 成 or front the result, or keep the agent as the subject as in the active English.