One may ask why to choose Seleucids out of all successors. There are certainly many interesting ones – especially if one looks at the wars between Diadochi. What differs Seleucids from others is their purchase / exchange of large quantity of Indian war elephants. They are not the small variety of african forest elephants that Hannibal imported over alps to amuse Romans, but substantially larger ones. Unlike Hannibal’s variety, they were heavily armored, tough and numerous.
War elephants were used as a shock weapon to terrorize and disorder enemy lines. There is no doubt that armored elephants carrying several men in howdahs were sight that put terror in heart of enemies not used to them. However, they were also effective charge weapon that could not be stopped easily – one only have to imagine rampaging animal of immense weight pushing forward with speed of nearly 30km/hour.
War elephants were very expensive, and only major powers could afford their own elephant corps. Elephants were likely first used in India due to obvious abundance of animal stock. Porus alone fielded around hundred against Alexander, and Nanda Empire or Gangaridai could probably field thousands of them, perhaps as many as 6000. Prospect of such powerful enemy forced even Alexander to rethink his Indian advances.
In west, use of elephants was more limited, and last battle where they were deployed in any significant number was battle of Thapsus 46 BC. In West, war elephants were seen in the ranks of Carthage, Phyrrus and Rome but in very limited numbers. After effective tactics were developed against them, elephants slowly fell out of favor and remained as viable weapon only in the East. Vietnamese used them still for combat role in 1885 during Sino-French war. After that, they were retained in armed service, but only in non-combat role for their ability to haul heavy loads.
These are successor elephants from Baccus, and I like them quite a lot. Since there ought to be two varieties, escorted and non-escorted, I should probably get another pair and have some odd javelin men around them. Additionally, elephants without howdah would probably serve better as Carthaginian / Roman variety so there might be place for some of those as well.