Currently, you can only summon one creature at a time in Siralim 3. While this was also the case in Siralim 2, in Siralim 3, having a large cast of creatures in your stable is much more important for game progression. In Siralim 3, one wants a large cast of creatures sitting in the stables, collecting XP and hitting the max level so you can breed them into ever higher Heredity levels as they hit the max level. You then want to replace those bred creatures with an even larger collection that essentially doubles each time you run out of the previous stock.
As it stands, the current most limiting factor in creating massive breeding stock is NOT the 2500 Brimstone/Crystal+2 cores that you need each time, or even the time extracting cores from a single type of creature. It’s the time summoning EACH and EVERY single one of the (eventually) HUNDREDS of stock you’ll need to hit those extremely high gene levels later on.
So, please allow us to summon multiple creatures at once. Huge QoL change!