Minecraft mob generator: /summon command

What to know about /summon

• Health is set by TWO fields, and this is the main trap. Health — this is current health, capped at maximum: zombies with Health:100f appears with twenty. The ceiling can only be raised via attribute max_health, so both are included in the command.
• Name — a text component, not a string. CustomName: "Boss" in modern game it doesn't work at all — the mob will remain unnamed. Therefore, name codes work as follows: &cGuardian will be red.
• Cubs of monsters and animals have different fields. For zombies IsBaby:1b, the cow's — age as a number (Age:-24000). IsBaby does nothing on cows.
• "No AI" and "Invulnerable" — this is a statue. The mob stays where it spawns, doesn't move, attack, or take damage. Used for decorative figures on spawn.
• Never disappear is required almost always. A regular mob vanishes when players are absent for a long time — and the arena boss will disappear before players arrive.
• Command compiled for 1.21.5 and newer. A second data format is intentionally omitted: entity fields have moved multiple times in different ways — ActiveEffects became active_effects in 1.20.5, attributes changed field names in 1.21, and the name from 1.21.5 is now an object (CustomName: {text: "Boss", color: "red"}), rather than a JSON string. Old syntax may appear literally above the mob's head. Only supported formats are offered here.
• Equipment is equipment, and not HandItems. From 1.21.5, items are stored in a compound 'slot → item', with probabilities in drop_chances. The command with old HandItems and ArmorItems will execute, and the mob will spawn naked. The old command can be inserted into import — equipment will transfer to the new entry.
• Default drop chance is 8.5%, and only from player hands. Normal drops may be damaged. Always uses a drop chance of 2.0, giving an undamaged item regardless of the cause of death; Never uses 0.0. Curse of Vanishing prevents the item from dropping.
• Effects on summoned mobs are set to infinite. Boss effects usually need to last beyond a short encounter. Disable Forever if you want an effect to expire after the selected duration.

The same mob, but inside a block that spawns it infinitely, will be collected mob spawner — it takes the base from here. Field names verified against Minecraft Wiki (Entity format, Commands/summon), equipment from client version 26.3; record for Java Edition 1.21.5+