The Sun is 333,000 Earth masses. It has an average density of 1408 kg/m^3. Its surface gravity is 274 m/s^2 and has an escape velocity of 617.6 km/s.
If a rogue planet is falling through the Sun's gravitational field, it will gain the equivalent of its escape velocity as it does so. Therefore, with an initial velocity of 30 km/s, the impact will be approximately 647.6 km/s. It will slam into a hot, dense medium. Heat released with the kinetic impact of the planet hitting the solar environment.
On its passage before crashing into the Sun, the rogue planet will be subject to radiant heating, it will be struck by solar flares, and it will have ploughed its way through the solar wind. These effects will be relatively minor compared to collision with the Sun, but the outer layers of the rogue planet will get very hot. Some material will be sloughed off its surface. The overall effect will depend on how it takes the planet to approach the bulk matter of the Sun.
The rogue planet will collide with a mass that is 27,750 greater than its own mass. The Sun is not a solid object. The planet will plunge into an extreme bath of hot plasma. The planet's kinetic energy will blast off its outer layers and it will be burning up like a meteor.
An interesting question may be whether the planet will survive sufficiently intact to slow down so that it sink into the depths of the Sun as it gradually evaporates. Once it is deep within the bulk of the Sun, after the kinetic ablation has stripped away its upper layers, it will be subject to a continuous plasma blow torch.
Will this collision have much impact on the Sun? Probably not. There are stars which have 'eaten' up to fifteen (15) Earth masses of terrestrial planets. This one too. The main difference is that these stars devoured their planets, they didn't undergo a collision.
The most likely outcome of a rogue planet collision with our Sun will be a spectacular display as the rogue planet plunges into the solar southern pole. Perhaps material sprayed up from the kinetic impact. Some effects on sunspots and solar flares. By and large, the mass differences will mean the Sun will come out unscathed, without any significant disruption. There will be changes in the Sun's composition. This will be interesting to astrophysicists.
Collisions like this sound more spectacular than they actually are. Stars like the Sun can easily swallow planets whole. A rogue planet with 12 Earth masses will be no exception.