summon spider ~ ~ ~ {Tags:["vb.custom_mob.baby_spider","vb.custom_mob","vb.loaded","vb.new_summon"]}

attribute @n[tag=vb.new_summon] minecraft:scale modifier add vb.mob_attribute -0.5 add_value
attribute @n[tag=vb.new_summon] minecraft:max_health modifier add vb.mob_attribute -4 add_value
attribute @n[tag=vb.new_summon] minecraft:movement_speed modifier add vb.mob_attribute 0.08 add_value

tag @n[tag=vb.new_summon] remove vb.new_summon