How would I combine it with water? Is it possible for an interaction to launch more than one material at a time?
They approach I used was multiple interactions, the key ones being liquid globs of water and a trailing vapor flow of "freeze juice" (ICEBOLT_ORC). Note Caste level homeotherm and fixed temp -- otherwise they'll kill themselves by frostbite.
[CASTE:FROSTSKALD_MALE]
[CASTE_NAME:frostskald:frostskalds:frostskald]
[CREATURE_CLASS:ORC_MALE]
[MALE]
[BODY_SIZE:0:0:3000] -- body size like a Goblin in masterwork
[BODY_SIZE:1:168:15000]
[BODY_SIZE:5:0:60000]
[HOMEOTHERM:10000]
[FIXED_TEMP:10000]
[PHYS_ATT_RANGE:STRENGTH:150:600:800:900:1000:1100:1500] - mediocre
[PHYS_ATT_RANGE:AGILITY:150:600:800:900:1000:1100:1500] - mediocre
[PHYS_ATT_RANGE:RECUPERATION:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[PHYS_ATT_RANGE:DISEASE_RESISTANCE:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[MENT_ATT_RANGE:ANALYTICAL_ABILITY:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[MENT_ATT_RANGE:FOCUS:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[MENT_ATT_RANGE:CREATIVITY:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[MENT_ATT_RANGE:INTUITION:2000:2500:3000:3250:3500:3750:4000] +++ quite good
[SKILL_LEARN_RATE:ALCHEMY:150]
[SKILL_LEARN_RATE:EXTRACT_STRAND:150]
[SKILL_LEARN_RATE:MAGIC_NATURE:150]
[NATURAL_SKILL:DIAGNOSE:3]
[NATURAL_SKILL:ALCHEMY:3]
[NATURAL_SKILL:EXTRACT_STRAND:3]
[NATURAL_SKILL:MAGIC_NATURE:5]
[CASTE_PROFESSION_NAME:STANDARD:frostskald:frostskalds]
[DESCRIPTION:A powerful humanoid creature with violent tendencies, Orcs build their strongholds in the twilight lands at the margins of the world. Frostskalds are Orcish Dreamwalkers who have learned to harness the stark fury of elemental ice. They turn this power against enemies foolish enough to encroach on their arctic homes.]
[CAN_DO_INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Hailstorm]
[CDI:USAGE_HINT:ATTACK]
[CDI:BP_REQUIRED:BY_CATEGORY:HAND]
[CDI:MATERIAL:INORGANIC:ICEBOLT_ORC:SOLID_GLOB]
[CDI:VERB:summons a driving hail:summons a driving hail:NA]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:TARGET_RANGE:C:20]
[CDI:MAX_TARGET_NUMBER:C:3]
[CDI:WAIT_PERIOD:300]
[CAN_DO_INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Arctic Gale]
[CDI:MATERIAL:INORGANIC:ICEBOLT_ORC:TRAILING_VAPOR_FLOW]
[CDI:USAGE_HINT:ATTACK]
[CDI:BP_REQUIRED:BY_CATEGORY:HAND]
[CDI:VERB:conjures a an arctic gale:conjures a an arctic gale:NA]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:TARGET_RANGE:C:10]
[CDI:MAX_TARGET_NUMBER:C:3]
[CDI:WAIT_PERIOD:300]
[CAN_DO_INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Waterbolt]
[CDI:USAGE_HINT:ATTACK]
[CDI:BP_REQUIRED:BY_CATEGORY:HAND]
[CDI:MATERIAL:WATER:LIQUID_GLOB]
[CDI:VERB:blasts with a stream of chill water:blasts with a stream of chill water:NA]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:TARGET_RANGE:C:20]
[CDI:MAX_TARGET_NUMBER:C:3]
[CDI:WAIT_PERIOD:300]
[CAN_DO_INTERACTION:MATERIAL_EMISSION]
[CDI:ADV_NAME:Cone of cold]
[CDI:USAGE_HINT:ATTACK]
[CDI:BP_REQUIRED:BY_CATEGORY:HAND]
[CDI:MATERIAL:WATER:WEB_SPRAY]
[CDI:VERB:invokes a crystalline ice spray:invokes a crystalline ice spray:NA]
[CDI:TARGET:C:LINE_OF_SIGHT]
[CDI:TARGET_RANGE:C:5]
[CDI:MAX_TARGET_NUMBER:C:1]
[CDI:WAIT_PERIOD:1000]
The weakness to cold (Chill blood) was among supplemental spell they could learn, which is why the syntax is a bit different here. It would slow enemies, and make them take more damage from both water and freeze juice (so "Icebolt", "Waterbolt", and "Hailstorm" would actually do a lot more damage). This is part of what lets them be fairly lethal to enemies while being just quite dangerous to allies.
[INTERACTION:CHILL_BLOOD_ORC]
[I_SOURCE:CREATURE_ACTION]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_REQUIRES:HAS_BLOOD]
[IT_MANUAL_INPUT:victim]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[IE_ARENA_NAME:chill blood]
[SYNDROME]
[SYN_NAME:chilled blood]
[CE_SPEED_CHANGE:SPEED_PERC:20:START:0:END:100]
[CE_SPEED_CHANGE:SPEED_PERC:40:START:101:END:300]
[CE_SPEED_CHANGE:SPEED_PERC:80:START:301:END:1000]
[CE_MATERIAL_FORCE_MULTIPLIER:MAT_MULT:INORGANIC:ICEBOLT_ORC:3:1:START:1:END:1000]
[CE_MATERIAL_FORCE_MULTIPLIER:MAT_MULT:WATER:3:1:START:1:END:1000]
The main property of ICEBOLT_ORC is that it has a really low melting and boiling point, so it comes out hella cold. The original "cryo" material that I learned this from also had syndromes built in to magic up some other special effects on the victims, which i didn't find necessary, but is another trick you could use.
[INORGANIC:ICEBOLT_ORC] # a syndrome-free version of "Cryo" by Gizogin
[DISPLAY_COLOR:3:0:1][TILE:'*']
[STATE_NAME:ALL_SOLID:ice]
[STATE_ADJ:ALL_SOLID:ice]
[STATE_COLOR:LIQUID:BLUE]
[STATE_NAME:LIQUID:freezing spray]
[STATE_ADJ:LIQUID:freezing spray]
[STATE_COLOR:GAS:BLUE]
[STATE_NAME:GAS:freezing vapor]
[STATE_ADJ:GAS:freezing vapor]
[MELTING_POINT:250]
[BOILING_POINT:2500]
[SOLID_DENSITY:12670]
[LIQUID_DENSITY:13300]
Hope it helps.