You can summon a Sniffer without any mod or resource pack using the command below.

To spawn a Sniffer, you have to obtain a Sniffer Spawn Egg. You have to throw a red dye and an egg to the ground to make a Sniffer Spawn Egg or right-click on the sign on the side of the command box that is written: "[​GIVE EGG]".

Watch on Youtube: https://youtu.be/1wdOd7dp5SI
Official command: https://torchcraftyt.github.io/Commands/Sniffer.html
Command on JustPaste.it: https://justpaste.it/sniffer

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Triple-click to select all the commands then right-click and choose copy. Next, get in your world, and give yourself a command block (using /give @s command_block). Paste the command in the command block (using Ctrl+C or Cmd+C). Finally, place a Redstone block next to the command block.

Command: (triple-click to select all)
summon minecraft:falling_block ~ ~1 ~ {BlockState:{Name:"redstone_block"},Time:1,Passengers:[{id:villager,Health:0,Passengers:[{id:falling_block,Time:1,BlockState:{Name:"activator_rail"},Passengers:[ {id:command_block_minecart, Command: 'gamerule commandBlockOutput false'}, {id:command_block_minecart, Command: 'scoreboard objectives add sniffer dummy'}, {id:command_block_minecart, Command: 'fill ~1 ~-2 ~0 ~13 ~1 ~3 minecraft:warped_nylium'}, {id:command_block_minecart, Command: 'fill ~1 ~-1 ~0 ~13 ~0 ~3 minecraft:red_stained_glass'}, {id:command_block_minecart, Command: 'setblock ~0 ~1 ~1 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"white",GlowingText:1b,Text1:\'{"text":"SNIFFER"}\',Text2:\'{"text":"COMMAND BOX"}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'}, {id:command_block_minecart, Command: '/setblock ~0 ~1 ~2 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"white",GlowingText:1b,Text1:\'{"text":"made by"}\',Text2:\'{"text":"TorchCraft"}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'}, {id:command_block_minecart, Command: '/setblock ~0 ~0 ~1 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"black",GlowingText:0b,Text1:\'{"color":"dark_blue","clickEvent":{"action":"run_command","value":"give @s salmon_spawn_egg{EntityTag:{id:armor_stand,Invisible:1b,Tags:[sniffer-spawner]},display:{Name:\\\'[{\\\\"text\\\\":\\\\"Sniffer Spawn Egg\\\\",\\\\"italic\\\\":false}]\\\'}} 1"},"text":"[GIVE EGG]"}\',Text2:\'{"text":""}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'}, {id:command_block_minecart, Command: '/setblock ~ ~ ~2 minecraft:oak_wall_sign[facing=west,waterlogged=false]{Color:"black",GlowingText:0b,Text1:\'{"color":"dark_red","clickEvent":{"action":"run_command","value":"fill ~ ~-2 ~-2 ~13 ~1 ~1 air"},"text":"[UNINSTAL]"}\',Text2:\'{"text":""}\',Text3:\'{"text":""}\',Text4:\'{"text":""}\'}'}, {id:command_block_minecart, Command: '/setblock ~2 ~-1 ~2 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"execute as @e[tag=sniffer-new] run scoreboard players operation @s sniffer = .index sniffer",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~3 ~-1 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"scoreboard players add .index sniffer 1",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~4 ~-1 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"tag @e remove sniffer-new",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~5 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-body] at @s unless entity @e[tag=sniffer-brain,distance=..4] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~6 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-leg3] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~7 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-leg2] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~8 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-leg1] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~9 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-body4] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~10 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-body3] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~11 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-body2] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~12 ~-1 ~2 minecraft:chain_command_block[conditional=false,facing=west]{Command:"/execute as @e[tag=sniffer-body1] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~2 ~-1 ~1 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-control] at @e[tag=sniffer-brain] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ~ ~ ~ ~ 0",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~3 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-head] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^-0.7 ^0.8 ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~4 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-body1] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^0.5 ^ ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~5 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-body2] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^0.5 ^-1 ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~6 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-body3] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^1.5 ^ ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~7 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-body4] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^1.5 ^-1 ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~8 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-leg1] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^ ^ ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~9 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-leg2] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^ ^-0.5 ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~10 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-leg3] at @e[tag=sniffer-control] if score @s sniffer = @e[limit=1,distance=0] sniffer run tp @s ^ ^ ^-1 ~ ~",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~11 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=east]{Command:"/execute as @e[tag=sniffer-control] at @s unless entity @e[tag=sniffer-brain,distance=..1] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~12 ~-1 ~1 minecraft:chain_command_block[conditional=false,facing=south]{Command:"/execute as @e[tag=sniffer-head] at @s unless entity @e[tag=sniffer-brain,distance=..2] run kill @s",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~2 ~0 ~2 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invisible:1b,NoBasePlate:1b,Invulnerable:1b,Tags:[sniffer-leg1,sniffer-new],ArmorItems:[{id:leather_boots,tag:{display:{color:4673362}},Count:1},{id:leather_leggings,tag:{display:{color:4673362}},Count:1}],ArmorDropChances:[0f,0f],DisabledSlots:4144959}",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~3 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invisible:1b,NoBasePlate:1b,Invulnerable:1b,Tags:[sniffer-leg2,sniffer-new],ArmorItems:[{id:leather_boots,tag:{display:{color:4673362}},Count:1},{id:leather_leggings,tag:{display:{color:4673362}},Count:1}],ArmorDropChances:[0f,0f],DisabledSlots:4144959}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~4 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invisible:1b,NoBasePlate:1b,Invulnerable:1b,Tags:[sniffer-leg3,sniffer-new],ArmorItems:[{id:leather_boots,tag:{display:{color:4673362}},Count:1},{id:leather_leggings,tag:{display:{color:4673362}},Count:1}],ArmorDropChances:[0f,0f],DisabledSlots:4144959}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~5 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invulnerable:1,Invisible:1,Marker:1,Tags:[sniffer-body1,sniffer-new],Passengers:[{id:falling_block,BlockState:{Name:\\"red_wool\\"},Time:-999999,NoGravity:1b,Tags:[sniffer-body]}]}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~6 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invulnerable:1,Invisible:1,Marker:1,Tags:[sniffer-body2,sniffer-new],Passengers:[{id:falling_block,BlockState:{Name:\\"red_wool\\"},Time:-999999,NoGravity:1b,Tags:[sniffer-body]}]}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~7 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invulnerable:1,Invisible:1,Marker:1,Tags:[sniffer-body3,sniffer-new],Passengers:[{id:falling_block,BlockState:{Name:\\"cyan_carpet\\"},Time:-999999,NoGravity:1b,Tags:[sniffer-body]}]}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~8 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invulnerable:1,Invisible:1,Marker:1,Tags:[sniffer-body4,sniffer-new],Passengers:[{id:falling_block,BlockState:{Name:\\"cyan_carpet\\"},Time:-999999,NoGravity:1b,Tags:[sniffer-body]}]}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~9 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invisible:1b,Tags:[sniffer-head,sniffer-new],ArmorItems:[{},{},{},{id:\\"minecraft:player_head\\",tag:{SkullOwner:{Id:[I;-1594983040,-2038738011,-1719167840,403061911],Properties:{textures:[{Value:\\"e3RleHR1cmVzOntTS0lOOnt1cmw6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvNDNmM2JlMDlhNzM1M2VlYWU5NGQ4ODMyMGNiNWIyNDJkZTJmNzE5YzBlNWMxNmE0ODYzMjdjNjA1ZGIxZDQ2MyJ9fX0=\\"}]}},display:{Lore:[\'{\\"text\\":\\"https://namemc.com/skin/8d62d734237840c7\\"}\']}},Count:1}],ArmorDropChances:[0f,0f,0f,0f],Invulnerable:1}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~10 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:panda ~ ~ ~ {MainGene:normal,HiddenGene:normal,Silent:1b,Tags:[sniffer-brain,sniffer-new],ActiveEffects:[{Id:14,Duration:999999,ShowParticles:0b}],CustomName:\'[{\\"text\\":\\"sniffer\\"}]\'}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~11 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"execute at @e[tag=sniffer-spawner] run summon minecraft:armor_stand ~ ~ ~ {Invisible:1b,Tags:[sniffer-control,sniffer-new],Invulnerable:1}",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~12 ~0 ~2 minecraft:chain_command_block[conditional=true,facing=east]{Command:"kill @e[tag=sniffer-spawner]",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~2 ~0 ~1 minecraft:repeating_command_block[conditional=false,facing=east]{Command:"/execute as @e[type=item,nbt={Item:{id:\\"minecraft:egg\\"}}] at @s if entity @e[limit=1,distance=..1,type=item,nbt={Item:{id:\\"minecraft:red_dye\\"}}] run tag @s add sniffer-spawnegg",auto:1b,conditionMet:1b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~3 ~0 ~1 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute as @e[tag=sniffer-spawnegg] run data modify entity @s Item set value {id:\\"minecraft:salmon_spawn_egg\\", Count:1b, tag: {EntityTag:{id:armor_stand,Invisible:1b,Tags:[sniffer-spawner]},display:{Name:\'[{\\"text\\":\\"Sniffer Spawn Egg\\",\\"italic\\":false}]\'}} }",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~4 ~0 ~1 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute as @e[tag=sniffer-spawnegg] at @s run particle minecraft:happy_villager ~ ~.3 ~ 0.1 0.1 0.1 1 10 normal",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~5 ~0 ~1 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute as @e[tag=sniffer-spawnegg] at @s run kill @e[type=item,limit=1,distance=..1,nbt={Item:{id:\\"minecraft:red_dye\\"}}]",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: '/setblock ~6 ~0 ~1 minecraft:chain_command_block[conditional=true,facing=east]{Command:"/execute as @e[tag=sniffer-spawnegg] at @s run tag @s remove sniffer-spawnegg",auto:1b,conditionMet:0b,powered:0b}'}, {id:command_block_minecart, Command: 'setblock ~ ~1 ~ command_block{Command:"fill ~ ~ ~ ~ ~-3 ~ air",auto:1}'}, {id:command_block_minecart, Command: 'kill @e[type=command_block_minecart,distance=..1,tag=!debug]'}, ]}]}]}