SCP-999 (The Tickle Monster), anyone?
It technically causes extreme pain when it tickles, but tickles actually work through stimulation of the pain receptors, and the effect is the same in any event. Happiness-causing interactions are currently impossible, so I made it boost its victims' social skills instead, as well as take away [CRAZED] and [OPPOSED_TO_LIFE] tags, which means it should (temporarially) be capable of calming down creatures like zombies and 682. It might even cure berserk dwarves, but I haven't checked on this.
[CREATURE:SCP-999]
[DESCRIPTION:A large, gelatinous mass of translucent orange slime that loves to tickle people.]
[NAME:tickle monster:tickle monsters:tickle monster]
[CASTE_NAME:tickle monster:tickle monsters:tickle monster]
[CREATURE_TILE:'T'][COLOR:6:0:1]
[PETVALUE:500]
[BIOME:ANY_TEMPERATE]
[BIOME:SUBTERRANEAN_CHASM]
[UNDERGROUND_DEPTH:2:3]
[POPULATION_NUMBER:15:30]
[CLUSTER_NUMBER:1:1]
[CHILD:2]
[MEANDERER][PET][LARGE_ROAMING][LIKES_FIGHTING]
[NO_DIZZINESS][NOBREATHE][EXTRAVISION][NOEXERT][NOFEAR][NONAUSEA][NOTHOUGHT][NO_THOUGHT_CENTER_FOR_MOVEMENT]
[BODY:AMEBOA_BODY]
[USE_MATERIAL_TEMPLATE:SKIN:SKIN_TEMPLATE]
[USE_MATERIAL_TEMPLATE:FLUID:CREATURE_EXTRACT_TEMPLATE]
[STATE_NAME:ALL_SOLID:frozen tickle monster slime]
[STATE_NAME_ADJ:ALL_SOLID:frozen tickle monster slime]
[STATE_NAME:LIQUID:tickle monster slime]
[STATE_NAME_ADJ:LIQUID:tickle monster slime]
[STATE_NAME:GAS:boiling tickle monster slime]
[STATE_NAME_ADJ:GAS:boiling tickle monster slime]
[STATE_COLOR:ALL:ORANGE]
[PREFIX:NONE]
[SYNDROME]
[SYN_NAME:tickled]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CREATURE:SCP-999:ALL]
[SYN_CONTACT]
[CE_PAIN:SEV:200:PROB:100:LOCALIZED:VASCULAR_ONLY:RESISTABLE:START:0:PEAK:50:END:100]
[SYNDROME]
[SYN_NAME:tickle monster euphoria]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CREATURE:SCP-999:ALL]
[SYN_CONTACT]
[CE_REMOVE_TAG:LIKES_FIGHTING:CRAZED:OPPOSED_TO_LIFE:START:0:END:1500]
[CE_MENT_ATT_CHANGE:EMPATHY:200:0:SOCIAL_AWARENESS:200:0:CREATIVITY:200:0:START:0:END:10000]
[TISSUE:SKIN]
[TISSUE_NAME:membrane:NP]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:SKIN]
[TISSUE_MAT_STATE:SOLID]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE:FLUID]
[TISSUE_NAME:fluid:NP]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:FLUID]
[TISSUE_MAT_STATE:LIQUID]
[MUSCULAR]
[FUNCTIONAL]
[STRUCTURAL]
[RELATIVE_THICKNESS:100]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:ALL:SKIN]
[TISSUE_LAYER_UNDER:BY_CATEGORY:ALL:FLUID]
[SECRETION:LOCAL_CREATURE_MAT:FLUID:LIQUID:BY_CATEGORY:ALL:SKIN]
[SPEED:900][SWIMS_INNATE][SWIM_SPEED:900]
[BODY_SIZE:0:0:1000]
[BODY_SIZE:2:0:54000]
[CAN_DO_INTERACTION:TICKLE]
[CDI:ADV_NAME:Tickle]
[CDI:BP_REQUIRED:BY_TYPE:GRASP]
[CDI:VERB:tickle:tickles:tickle each other]
[CDI:CAN_BE_MUTUAL]
[CDI:TARGET:A:SELF_ONLY]
[CDI:TARGET:B:TOUCHABLE]
[CDI:TARGET_RANGE:B:1]
[CDI:MAX_TARGET_NUMBER:B:1]
[CDI:WAIT_PERIOD:5]
[FREE_ACTION]
[CASTE:FEMALE]
[FEMALE]
[CASTE:MALE]
[MALE]
[SELECT_CASTE:ALL]
[SET_TL_GROUP:BY_CATEGORY:ALL:SKIN]
[TL_COLOR_MODIFIER:CLEAR:1]
[TLCM_NOUN:membrane:SINGULAR]
[SET_TL_GROUP:BY_CATEGORY:ALL:FLUID]
[TL_COLOR_MODIFIER:ORANGE:1]
[TLCM_NOUN:interior:SINGULAR]
[INTERACTION:TICKLE]
[I_SOURCE:CREATURE_ACTION]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_BP]
[I_TARGET:B:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_MANUAL_INPUT:creature]
[I_EFFECT:CONTACT]
[IE_TARGET:A]
[IE_TARGET:B]
[IE_IMMEDIATE]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:B]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_NAME:tickled]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CREATURE:SCP-999:ALL]
[CE_PAIN:SEV:10000000:PROB:100:VASCULAR_ONLY:RESISTABLE:START:0:PEAK:50:END:100]
[SYNDROME]
[SYN_NAME:tickle monster euphoria]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CREATURE:SCP-999:ALL]
[CE_REMOVE_TAG:LIKES_FIGHTING:CRAZED:OPPOSED_TO_LIFE:START:0:END:1500]
[CE_MENT_ATT_CHANGE:EMPATHY:200:0:SOCIAL_AWARENESS:200:0:CREATIVITY:200:0:START:0:END:10000]
[BODY:AMEBOA_BODY]
[BP:HD:body:bodies][UPPERBODY][LOWERBODY][HEAD][LIMB][GRASP][CATEGORY:HEAD]
[DEFAULT_RELSIZE:2000]