Examples

Example 1 : Cactus familiar

Here is an example of a full upgraded familiar. This is just an example, the familiar itself is useless (and his upgrades as well).

local CactusMod = RegisterMod("Cactus", 1);

CactusMod.CollectibleID = Isaac.GetItemIdByName("Cactus")
CactusMod.FamiliarVariant = Isaac.GetEntityVariantByName("Cactus")


-- Default cactus behaviour
function CactusMod:CactusUpdate(cactus)
    if cactus.FrameCount % 60 == 0 then
        Isaac.Spawn(EntityType.ENTITY_EFFECT, EffectVariant.PLAYER_CREEP_GREEN, 0, cactus.Position, Vector(0, 0), cactus)
    end
end
-- Cactus behaviour when upgraded (super and ultra)
function CactusMod:CactusUpdateUpgraded(cactus)
    if cactus.FrameCount % 90 == 0 then
        local amountOfTears = 6
        if Sewn_API:IsUltra(cactus:GetData()) then
            amountOfTears = 10
        end
        for i = 1, amountOfTears  do
            local velocity = Vector(6, 6)
            velocity = velocity:Rotated((360 / amountOfTears ) * i)
            local tear = Isaac.Spawn(EntityType.ENTITY_TEAR, TearVariant.BLOOD, 0, cactus.Position, velocity, cactus)
        end
    end
end

-- Cactus get out of Sewing Machine
function CactusMod:CactusGetFromMachine(cactus, player, sewingMachine, isUpgraded, newLevel)
    if isUpgraded and newLevel == Sewn_API.Enums.FamiliarLevel.ULTRA then
        -- Spawn a blue spider when upgraded
        Isaac.Spawn(EntityType.ENTITY_FAMILIAR, FamiliarVariant.BLUE_SPIDER, 0, cactus.Position, Vector(0, 0), cactus)
    end
end

-- On new room for Ultra cactus
function CactusMod:CactusNewRoom(cactus)
    local sprite = cactus:GetSprite()
    -- Play the dance animation on new room
    sprite:Play("Dance", true)
end

-- Standard "familiar update" callback
CactusMod:AddCallback(ModCallbacks.MC_FAMILIAR_UPDATE, CactusMod.CactusUpdate, CactusMod.FamiliarVariant)

if Sewn_API then -- If Sewing Machine is enabled
    -- Make the familiar available for Sewing Machine
    Sewn_API:MakeFamiliarAvailable(CactusMod.FamiliarVariant, CactusMod.CollectibleID)

    -- Add an EID description
    Sewn_API:AddFamiliarDescription(
        CactusMod.FamiliarVariant,
        "Fire tears in all directions every 3 seconds",
        "Fire more tears every 3 seconds#Dance when clearing a room"
    )
    -- Add Encyclopedia support
    Sewn_API:AddEncyclopediaUpgrade(
        CactusMod.FamiliarVariant,
        nil, -- nil to add the default EID description for super upgrade
        "Fire 10 tears instead of 6 every 3 seconds#Dance when clearing a room for no reasons",
        "This is a test familiar, no mods use it...for now"
    )

    -- Add more callbacks
    -- This isn't required, you can do all the logic in the standard "MC_FAMILIAR_UPDATE" callback

    -- This callback will be called for SUPER and ULTRA by default
    Sewn_API:AddCallback(Sewn_API.Enums.ModCallbacks.FAMILIAR_UPDATE, CactusMod.CactusUpdateUpgraded, CactusMod.FamiliarVariant)
    Sewn_API:AddCallback(Sewn_API.Enums.ModCallbacks.POST_GET_FAMILIAR_FROM_SEWING_MACHINE, CactusMod.CactusGetFromMachine, CactusMod.FamiliarVariant)
    -- This callback will be called for ULTRA only
    Sewn_API:AddCallback(Sewn_API.Enums.ModCallbacks.POST_FAMILIAR_NEW_ROOM, CactusMod.CactusNewRoom, CactusMod.FamiliarVariant, Sewn_API.Enums.FamiliarLevelFlag.FLAG_ULTRA)
end

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For more on how to use the Sewing Machine API, you can see the code in the mod folder. Every familiars can be found in Sewing machine/sewn_scripts/entities/familiar/upgrades/vanilla