Lots and lots of damage to electrical components. It does not take long for the smoke to come out.

Check fuses ... you might get lucky.

The voltage regulator/rectifier is another common victim when this happens.

Have you tried to start it with the battery connected correctly ?
I'm thinking the damage is already done.

It's likely that at least some of your electronics, including the engine control are damaged.

TTFN (ta ta for now)
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Older electronics modules in vehicles frequently could not handle reverse polarity on their internal voltage regulators. More recent electronics are more likely to be able to withstand reverse polarity. The exception in more modern electronics are power drivers for solenoids and motors (power MOSFET) which have an inherent reverse diode that will conduct. These are frequently arranged in groups of four to drive a motor in either direction, called a H-Bridge arrangement. For these, the inherent diodes will represent a direct short when you applied reverse polarity. The module doesn't even need to be activated for reverse polarity to zap MOSFETs in an H-bridge arrangement under reverse polarity. There are also power ICs that have the H-Bridge MOSFETs internally.

If you really did only connect the battery for one second, then you may be lucky and didn't apply reverse power long enough for these MOSFETs to overheat and blow. Since fuses in cars are slow acting, I don't think they could act fast enough to protect these.

Check every motor, small or large, in the car that can run bi-directionally and is controlled by a non-relay electronics module. These would be the modules most likely to get damaged.