Serpifero

If Spawnwrithe’s ability triggers, then Spawnwrithe becomes a copy of another creature before its ability resolves (due to Mirrorweave, perhaps), the token will be a copy of whatever creature the Spawnwrithe is currently a copy of. At the end of the turn, Spawnwrithe will revert back to what it was, but the token will stay as it is.

As the token is created, it checks the printed values of the Spawnwrithe it’s copying — or, if the Spawnwrithe whose ability triggered was itself a token, the original characteristics of that token as stated by the effect that put it onto the battlefield — as well as any copy effects that have been applied to it. It won’t copy counters on the Spawnwrithe, nor will it copy other effects that have changed Spawnwrithe’s power, toughness, types, color, or so on. Normally, this means the token will simply be a Spawnwrithe. But if any copy effects have affected that Spawnwrithe, they’re taken into account.

A token created by a Cemetery Puca that’s copying a Spawnwrithe will be a Spawnwrithe with the Cemetery Puca ability.

If a copy effect such as Mirrorweave causes some other creature to become a copy of Spawnwrithe, then that creature deals combat damage to a player, the token that’s put onto the battlefield is simply a copy of Spawnwrithe.