unionall.ssb is a file, containing the game's coroutines. Those coroutines are used to show a cutscenes, return controls to the player after the dialogue with NPC, make a Cutscene -> Overworld transition etc.
You can call those coroutines with CallCommon, JumpCommon, ExecuteCommon and supervision_ExecuteCommon opcodes.
Coroutines
coro END_TALK
coro WAIT_START_FUNC
coro NORMAL_WAIT_END_TALK
coro LIVES_REPLY_NORMAL
coro LIVES_REPLY
coro OBJECT_REPLY_NORMAL
coro LIVES_ACTING_NORMAL
coro ENTER_WAIT_FUNC
coro TALK_UNIT
coro TALK_ADVENTURE
coro TALK_ATTENDANT
coro TALK_PARTNER_MESSAGE
coro LIVES_MOVE_NORMAL
coro LIVES_MOVE_CHANGE=
coro LIVES_MOVE_PARTY
coro OBJECT_MOVE_NORMAL
coro OBJECT_MOVE_CHANGE
coro PERFORMER_MOVE_NORMAL
coro PERFORMER_MOVE_CHANGE
coro MOVE_INIT
coro MOVE_PAUSE
coro MOVE_STAY
coro MOVE_SLEEP
coro MOVE_RANDOM
coro MOVE_TYPE1
coro MOVE_TYPE2
coro WAKEUP_FUNC
coro WAKEUP_FUNC_SERIES
coro LOOK_AROUND_FUNC
coro LOOK_AROUND_FUNC_SERIES