You could quite easily make a 'captive breeding pack' using animals either in or recommended for captive breeding in the Annamite Mountains of Vietnam and Laos - unfortunately, a lot of the endemic species there are on the brink of extinction now.
1. Vietnamese crested argus - This critically endangered pheasant has the longest and broadest tail feathers of any bird, which it uses in its courtship display that is much like that of the great argus. They have been kept and bred in captivity since the 90s at Saigon Zoo, so they definitely represent a species which can survive in zoos. As far as I could find, the only place that keeps Vietnamese crested argus outside of their native range is in Japan.
2. Large-antlered muntjac - A secondary function for a saola breeding centre being constructed in Vietnam's Bach Ma National Park is to establish a conservation programme for the critically endangered large-antlered or giant muntjac, the biggest of the muntjac deer. While their population is following the same trajectory as the saola (as in plummeting), there are still a few places where they can be quite easily found, so locating and bringing them into the breeding centre would be easier, making them the best choice for an ungulate in this type of pack.
3. Annamite striped rabbit - Only discovered in 1996, this brightly coloured jungle rabbit is, like most smaller mammals, at high risk of snaring and so is listed as endangered. The IUCN has recommended that a captive breeding programme is established for this species in the near future, while their populations remain large enough so as to be detectable and in order to learn how they can be kept in case their population declines even further - their only relative, the Sumatran striped rabbit, has been kept successfully in European zoos in the past.
4. A douc langur - While the red-shanked douc is now kept in two zoos in Europe, they are bred in a number of zoos in their native range. The Endangered Primate Rescue Centre in Cuc Phuong National Park breeds not only red-shanked but the grey-shanked and black-shanked doucs (I haven't heard of anywhere else keeping these two species). They are colourful, sociable, highly endangered, can be bred in captivity and, almost uniquely among monkeys, would also use the brachiation climbing frame.
Exhibit. Vietnamese big-headed turtle - As far as I know, there is only one individual kept in a zoo outside of Vietnam (a male, imported to Norden's Ark in Sweden in 2021). They are bred in the Turtle Conservation Centre, also at Cuc Phuong National Park. This is a subspecies of the more widespread and widely-kept big-headed turtle, which has a head so large it cannot retreat into its shell, and is unusual among turtles in that it can climb waterfalls and even climb trees.
Alternative. Saola - Both the most obvious option and potentially the worst. Although construction on the Bach Ma breeding centre started in 2017, the animal was last recorded in the wild in 2013 and could possibly already be extinct. They are a beautiful animal and, perhaps surprisingly considering its rarity, there have been enough behavioural observations of earlier captive animals made that a pretty good likeness of the saola could be recreated in the game but their doubtful continued survival makes it difficult to recommend this species.
Another option, massively preferable to the saola for me personally, could be the
Owston's civet - although they are kept in four UK zoos, the bulk of their captive population is in the Carnivore and Pangolin Conservation Centre, again in Cuc Phuong National Park. They are a beautiful species, which conservationists have recently determined requires captive breeding for its continued survival.
Such a pack could be used to raise awareness of the species themselves (which not many people have heard of) and the organisations working to protect these species:
The Carnivore and Pangolin Programme:
https://svw.vn/conservation-breeding/
The Endangered Primate Rescue Centre:
https://www.eprc.asia/
The Turtle Conservation Centre:
https://asianturtleprogram.org/turtle-conservation-centre/
