you can put the mobs to level up in conf folder.
you can add in monster spawn script (each spawn of each map) the AI mode.
** Create a permanent monster spawn:
<map name>,<x>,<y>{,<xs>{,<ys>}}%TAB%monster%TAB%<monster name>{,<monster level>}%TAB%<mob id>,<amount>{,<delay1>{,<delay2>{,<event>{,<mob size>{,<mob ai>}}}}}
Map name is the name of the map the monsters will spawn on. x,y are the
coordinates where the mob should spawn. If xs and ys are non-zero, they
specify the 'radius' of a spawn-rectangle area centered at x,y.
Putting zeros instead of these coordinates will spawn the monsters randomly.
Note this is only the initial spawn zone, as mobs random-walk, they are free
to move away from their specified spawn region.
Monster name is the name the monsters will have on screen, and has no relation
whatsoever to their names anywhere else. It's the mob id that counts, which
identifies monster record in 'mob_db.txt' database of monsters. If the mob name
is given as "--ja--", the 'japanese name' field from the monster database is
used, (which, in rAthena, actually contains an English name) if it's "--en--",
it's the 'english name' from the monster database (which contains an uppercase
name used to summon the monster with a GM command).
You can specify a custom level to use for the mob different from the one of
the database by adjoining the level after the name with a comma. eg:
"Poring,50" for a name will spawn a monster with name Poring and level 50.
Amount is the amount of monsters that will be spawned when this command is
executed, it is affected by spawn rates in 'battle_athena.conf'.
Delay1 and delay2 control monster respawn delays - the first one is the fixed
base respawn time, and the second is random variance on top of the base time.
Both values are given in milliseconds (1000 = 1 second).
Note that the server also enforces a minimum respawn delay of 5 seconds.
Event is a script event to be executed when the mob is killed. The event must
be in the form "NPCName::OnEventName" to execute, and the event name label
should start with "On". As with all events, if the NPC is an on-touch NPC, the
player who triggers the script must be within 'trigger' range for the event to
work.
There are two optional fields for monster size and AI.
<mob size> can be:
Size_Small (0)
Size_Medium (1)
Size_Large (2)
<mob ai> can be:
AI_NONE (0) (default)
AI_ATTACK (1) (attack/friendly)
AI_SPHERE (2) (Alchemist skill)
AI_FLORA (3) (Alchemist skill)
AI_ZANZOU (4) (Kagerou/Oboro skill)
AI_LEGION (5) (Sera skill)
AI_FAW (6) (Mechanic skill)
Alternately, a monster spawned using 'boss_monster' instead of 'monster' is able
to be detected on the map with the SC_BOSSMAPINFO status (used by Convex Mirror).
You can check the full file in doc folder:
https://github.com/rathena/rathena/blob/master/doc/script_commands.txt