Defined in macros/scripts/events.asm and engine/overworld/scripting.asm:ScriptCommandTable .
Until this document is filled out, the G/S Scripting Compendium has descriptions for most of these commands. It was written for G/S binary hacking and not Crystal assembly hacking, so it's not 100% accurate for pokecrystal.
$06
: ifequal byte , script
$07
: ifnotequal byte , script
$0A
: ifgreater byte , script
$0F
: special special_pointer
$12
: setmapscene map , scene_id
$19
: copybytetovar address
$1A
: copyvartobyte address
$1B
: loadvar address , value
$1D
: writevarcode variable
$1E
: writecode variable , value
$1F
: giveitem item_id [, quantity =1]
$20
: takeitem item_id [, quantity =1]
$22
: givemoney account , value
$23
: takemoney account , value
$24
: checkmoney account , value
$28
: addcellnum contact_id
$29
: delcellnum contact_id
$2A
: checkcellnum contact_id
$2D
: givepoke mon_id , level [, item =0[, trainer =0, ot_name , nickname ]]
$2E
: giveegg mon_id , level
$2F
: givepokemail pointer
$30
: checkpokemail pointer
$31
: checkevent event_flag
$32
: clearevent event_flag
$34
: checkflag engine_flag
$35
: clearflag engine_flag
$3A
: warpmod warp_id , map
$3D
: readmoney account , memory
$40
: pokenamemem mon_id , memory
$41
: itemtotext item_id , memory
$42
: mapnametotext memory
$43
: trainertotext trainer_id , trainer_group , memory
$44
: stringtotext text_pointer , memory
$48
: refreshscreen [dummy =0]
$4B
: farwritetext text_pointer
$4C
: writetext text_pointer
$4D
: repeattext byte1 , byte2
$4F
: loadmenu menu_header
$51
: jumptextfaceplayer text_pointer
$52
: farjumptext text_pointer
$53
: jumptext text_pointer
$58
: _2dmenu
$59
: verticalmenu
$5D
: loadwildmon mon_id , level
$5E
: loadtrainer trainer_group , trainer_id
$60
: reloadmapafterbattle
$62
: trainertext which_text
$63
: trainerflagaction action
$64
: winlosstext win_text_pointer , loss_text_pointer
$68
: setlasttalked object_id
$69
: applymovement object_id , data_pointer
$6A
: applymovement2 data_pointer
$6C
: faceobject object1 , object2
$6D
: variablesprite variable_sprite_id , sprite_id
$70
: follow object2 , object1
$72
: moveobject object_id , x , y
$73
: writeobjectxy object_id
$75
: showemote emote_id , object_id , length
$76
: turnobject object_id , facing
$77
: follownotexact object2 , object1
$79
: changemap bank , blockdata_pointer
$7A
: changeblock x , y , block
$7D
: writecmdqueue queue_pointer
$81
: musicfadeout music_id , length
$89
: passtoengine data_pointer
$8A
: newloadmap which_method
$8C
: deactivatefacing length
$8F
: ptpriorityjump script
$92
: reloadandreturn which_method
$94
: pokemart dialog_id , mart_id
$97
: askforphonenumber contact_id
$9A
: describedecoration byte
$9C
: specialphonecall call_id
$9E
: verbosegiveitem item_id [, quantity =1]
$9F
: verbosegiveitem2 item_id , variable
$A3
: warpfacing facing , map , x , y
$A4
: battletowertext memory
$A5
: landmarktotext landmark_id , memory
$A6
: trainerclassname trainer_group , memory
$A7
: name type , id , memory