Hold Person
The OSRIC spell description says this:
Persons held by this spell may be killed or bound at a rate of one per round, or, if the attacker chooses, may be attacked at twice the normal rate with an automatic hit, for maximum damage.From all I can gather, hold person completely immobilizes the opponent. They have no ability to react whatsoever, therefore automatic kills are allowed. In fact, I think it’s probably correct to rule that held individuals aren’t even able to speak.
Entangle
Sourcing OSRIC again:
[If] the saving throw fails, the creature is so securely held in the plants that it cannot move, attack, or cast spells for the duration of the spell.This is a little more gray, however I don’t interpret this as the degree of helplessness indicated by hold person. First off, the individual is only “held” as securely as the foliage can wrap them (as opposed to being outright frozen in place). Secondly, it’s reasonable to think that the entangling plants themselves may obstruct the target area for an insta-kill attempt (like the throat). Third, anyone engaging in melee with an entangled foe obviously needs to make a conscious attempt to not succumb to the entanglement themselves.
I think a fair ruling on this spell is that magically entangled opponents are considered prone:
Prone Opponent: Attacks against a prone opponent negate the benefit of a shield, negate dexterity bonuses, and are made at +4 to hit.
Magically sleeping creatures may be killed or tied up at a rate of one per round by a single person, or can be attacked at twice the normal rate with an automatic hit for maximum damage, if the attacker chooses not to kill or bind them.
Sleeping Opponent: Sleeping opponents (natural sleep, not magical sleep) may be attacked with the same chance to kill as if the attacker were an assassin. The effect of magical sleep is described under the entry for the sleep spell.

