Diablo II: Lord of Destruction/Summoning

Increasing the number of minions in your party can never hurt, and this branch of the druid's skill tree does that in spades. Some minions directly attack the enemy, while others augment the druid's already existing skills and life and mana supply. All minions (apart from the airborne raven) serve to distract enemies at no cost to the druid's personal health, making them very useful to players who dislike, or cannot afford, dying.

Certain summonings can cancel previous summonings; for example, a druid may have active only one type of vine (poison creeper, carrion vine, or solar creeper), one type of spirit (oak sage, heart of wolverine, or spirit of barbs), and one type of ground creature (spirit wolf, dire wolf, or grizzly). Ravens are not dispelled when wolves or bears are present.

Vines creep along behind their druid, performing their particular skills at their own discretion. Spirits tag along, casting their helpful auras on any party member near enough to be affected. Summoned creatures generally follow the druid but choose their own targets, and they will often attack without waiting for the druid himself to make contact.

Raven
Ravens cannot be damaged by enemies, thanks to their wings, guaranteeing that when you summon them, you will benefit from their attacks. A raven can also attack across gaps where wolves and grizzlies cannot roam.
 * Description: Summons a raven (or more than one, depending on skill level) that attacks a certain number of times before vanishing
 * Level prerequisite: 1
 * Skill prerequisite: None
 * Mouse button: Right

Poison Creeper
This low-level vine is most useful in the early game and against enchanted monsters, since poison damage doesn't take full effect immediately. Most players replace the creeper with more powerful vines when they can do so.
 * Description: A vine that does poison damage to its own targets
 * Level prerequisite: 1
 * Skill prerequisite: None
 * Mouse button: Right

Oak Sage
A high-level oak sage is a tremendous boon to a party, especially a group of hardcore characters. An oak sage needs a moment before its life-giving benefit takes effect, but when it does, it automatically fills each party member's life globe as it increases the maximum life level. A powerful oak sage can make a high-level character extremely difficult to kill.
 * Description: A spirit that boosts the life level of the druid and all members of his party
 * Level prerequisite: 6
 * Skill prerequisite: None
 * Mouse button: Right

Summon Spirit Wolf
A spirit wolf makes a good early-game minion, but more advanced creature-summoning skills will likely take its place once they are available.
 * Description: Calls forth a spirit wolf, who assists in a druid's attacks
 * Level prerequisite: 6
 * Skill prerequisite: Raven
 * Mouse button: Right

Carrion Vine
This vine sucks the last bit of life out of corpses and gives it to the druid. This ruins the corpses for necromancers (who can raise the dead as minions) and barbarians (who can search the dead for potions and items), and there is no way to directly unsummon a carrion vine. However, summoning a poison creeper will cause the carrion vine to disappear, and the creeper has no effect on corpses. A carrion vine requires an unshattered corpse in order to be effective, so bear this in mind when using such a vine while you attack with cold damage.
 * Description: A vine that consumes fallen enemies and transfers the life to the casting druid
 * Level prerequisite: 12
 * Skill prerequisite: Poison Creeper
 * Mouse button: Right

Heart of Wolverine
This skill is primarily for offensively minded druids who wish to augment the attack rating and damage of all party members. Only one spirit may be present at a time, so summoning this spirit will cancel all others.
 * Description: A spirit that boosts the offensive skills of a druid and his party members
 * Level prerequisite: 18
 * Skill prerequisite: Oak Sage
 * Mouse button: Right

Summon Dire Wolf
The dire wolf is a tougher version of the spirit wolf and will assist the druid by attacking its own chosen targets. It's a good minion for the midgame, until the grizzly becomes available, and it may be a better choice if you prefer the multiple minions provided by playing more skill points into dire wolf.
 * Description: Calls forth a dire wolf, who assists in a druid's attacks
 * Level prerequisite: 18
 * Skill prerequisite: Oak Sage, Summon Spirit Wolf
 * Mouse button: Right

Solar Creeper
This vine is more sentient than the carrion vine, which feeds on corpses regardless of the druid's health. A solar creeper will wait to feast on fallen enemies until the druid requires mana. This vine is especially beneficial to druids who use mana-intensive spells like hurricane and armageddon. Switch to carrion vine when life, not mana, is in short supply.
 * Description: A vine that sucks the mana from corpses and adds it to the druid's supply
 * Level prerequisite: 24
 * Skill prerequisite: Carrion Vine
 * Mouse button: Right

Spirit of Barbs
Much like a paladin's thorns skill, spirit of barbs harms any enemy that successfully causes damage to a party member.
 * Description: A spirit that reflects damage back at attacking enemies who score hits on party members
 * Level prerequisite: 30
 * Skill prerequisite: Heart of Wolverine
 * Mouse button: Right

Summon Grizzly
Truly a ferocious comrade, the grizzly absorbs the toughest onslaughts while his druid summoner assists him with spellcasting. Grizzlies stay alive better than any other summoned creature. Alas, it's only one pal and it may not occupy an entire group of enemies like several dire wolves may. Purchase a hireling at camp to assist the powerful grizzly if you're attempting the game alone.
 * Description: Summons a grizzly bear, which assists in a druid's attacks
 * Level prerequisite: 30
 * Skill prerequisite: Summon Dire Wolf
 * Mouse button: Right