From the Jain point of view, exact future udaya cannot be predicted for one single act, because bondage depends on many factors: intention, passions, intensity, duration, and accumulation of other karmas. But in general, the principles are clear.

1) If one knowingly kills a panchendriya jīva, what karma is bound?

If the act is knowing, intentional, and done with carelessness or passions, then very heavy pāpa-bandha occurs.

The main bond is not just one karma type; rather, the soul binds:

• Asrava and bandha of pāpa karma
• Strong mohaniya karma because anger, fear, delusion, and attachment are involved
• Āyu karma may become unfavorable according to the overall karmic state
• Nāma karma and gotra karma may also be affected
• The act also increases ghora hiṃsā-bandha because a panchendriya jīva has the highest developed senses

In Jain ethics, the main strength of bondage depends on:

• knew or did not know
• wanted the harm or not
• negligence / pramāda
• kashāya: anger, pride, deceit, greed
• actual injury caused

So, knowingly killing a panchendriya jīva is considered very grave hiṃsā.

2) If one does prāyaścitta for that sin, what happens?

Prāyaścitta does not erase the past act, but it helps in important ways:

• It reduces future bondage
• It weakens the force of the sinful impression
• It helps burn or lighten the effect through repentance, confession, and restraint
• It creates vigilance, so similar harm is less likely in future
• It purifies the mind if done with true remorse and humility

In Jain dharma, prāyaścitta becomes fruitful when there is:

• honest confession
• inner regret
• acceptance of fault
• determination not to repeat the act
• obedience to the prescribed penance

If the outer penance is done but the mind remains careless or proud, the benefit is much less.

3) If prāyaścitta had not been taken, what could happen?

If no prāyaścitta and no repentance were done, then the karma would generally remain heavier and stronger.

That means:

• the sinful impression stays stronger in the soul
• there is greater chance of future udaya of painful experiences
• the mind becomes more accustomed to negligence
• the same type of fault may repeat in later circumstances

In Jain understanding, karmas can come into udaya later as:

• suffering
• fear
• separation
• injury
• obstacles
• disturbed states of mind
• situations where one faces similar helplessness or harm

But again, the exact form and birth are not fixed from one act alone. They depend on the whole karmic account.

4) Regarding your specific situations

A) Bats in the room

If you knew living beings were there and still acted in a way that could harm them, then there is some intentional or negligent hiṃsā-bandha. Because bats are panchendriya jīvas, the act is serious.

If later you confessed and took prāyaścitta, that is spiritually good. It shows:

• awareness
• remorse
• responsibility
• desire for purification

B) Lizard in the zipped bag

If you truly did not know the lizard was inside, then the bondage is lighter than deliberate killing. Still, since a living being died through the act, there can be bondage through carelessness.

Your prāyaścitta was appropriate.

C) Watermelon juice and ants

This is also karmically relevant, but generally less severe than panchendriya-himsa. Ants are jīvas, and harming them through negligence still binds karma.

Taking prāyaścitta with sincerity helps purify that bond.

5) The main Jain principle

In Jain dharma, karma binds mainly through:

• yoga: activity of mind, speech, body
• kashāya: passions
• pramāda: negligence

So the same outward act can bind very different karma depending on the inner state.

In simple terms:

• More intention + more passion + more negligence = heavier bondage
• Less intention + less passion + repentance = lighter bondage

6) Final spiritual point

What matters now is not despair, but awakening.

If you have:

• confessed
• felt true remorse
• taken prāyaścitta
• become more careful

then that is the Jain path of purification.

Prāyaścitta is meant to soften the soul, stop future hiṃsā, and reduce bondage. It is not just punishment; it is inner cleansing.

If you want, I can also give this in a very short Jain-style summary.