Omastar have only just recently been evolved.

As there were not many omanyte that have been used in battle there wasn't much chance for one to evolve, until now.
4 have evolved and are currently being studied.

However now their are 4 omastar a breeding program can be set up as omanyte cannot breed. this means far more omanyte and Omastar's and their is even talk of re-releasing them into the wild.

Four of their tentacles (after evolving) become almost like hands, and double in strength. the others become smaller but have light numbing poisons in them which helps when catching prey. It is thought they grab their prey with the smaller tentacles, numbing and pulling it in, then the larger ones grab hold and pull them into their powerful four beaked mouth.

Omastar are a little dangerous. they have been proved to be aggressive and their beaks can near cut through steel.
The west cerulean aquarium found this out the hard way when they bought the second omastar ever to be evolved as a special display. the tank was at first too small and the Omastar smashed the glass and gnawed through the steel plating.
They then spent a huge amount of money creating a reinforced tank. However they do not appear to be aggressive towards humans and seem very interested in them rather than hunting them. It is not known how large they truly grow but the largest found in the fossil records was the size of a minivan.

Hope you like it