To successfully summon phantoms for cooperative play in Dark Souls 3, there are specific conditions and procedures you need to follow. Here’s a detailed guide that outlines both cooperative summoning and PvP invasions.

Summoning Phantoms for Cooperative Play

1. Enter Ember Form:
– First, you need to use an Ember to enter the “Lord of Cinder” state. This transformation is essential for initiating multiplayer sessions, enabling the summoning and hosting of other players [3].

2. Use the White Sign Soapstone:
– Acquire the White Sign Soapstone to place your summon sign on the ground. This allows other players to summon you into their worlds as a friendly phantoms, known as “white phantoms” [1][5].

3. Summoning a White Phantom:
– To summon someone into your world, simply stand over their White Summon Sign and interact with it. This action will bring them into your game to assist you [1].

4. Set a Multiplayer Password:
– For easier connection to specific friends, set a multiplayer password through the game menu. This feature allows you to bypass the game’s normal level matchmaking system, ensuring you can summon your friends more reliably [2][5].

5. Post-Boss Summoning Restrictions:
– Be aware that immediately after a central area boss has been defeated, co-op summon signs (both white and yellow) will not be visible in that area, except for hostile PvP phantoms (purple signs) such as those from the Mound-Makers covenant [1].

6. Matchmaking Criteria:
– The game generally matches players based on their level and weapon upgrades, typically allowing players within a 20-level range of each other to connect [1][3].

Engaging in PvP Invasions

1. Invasion Items:
– Use specific invasion items or participate in covenant activities to invade other players’ worlds. This is crucial for initiating PvP encounters.

2. Red Sign Soapstone:
– The Red Sign Soapstone enables you to leave a sign that allows others to summon you as a hostile invader. Conversely, you can also invade by using other players’ red signs [2].

3. Targeted PvP:
– You can also conduct invasions in a more targeted manner by setting a password, making it easier to engage specific friends in duels [2].

4. Using the Dried Finger:
– The Dried Finger resets the invasion cooldown, enabling you to invite more phantoms (up to three cooperators) into your world, although this increases the likelihood of facing more invaders [3].

5. Fair Matchmaking:
– Similar to co-op play, PvP invasions and matchmaking also follow the level and weapon upgrade criteria for fairer encounters [3].

Summary Table

| Activity | Required Item/Condition | Description |
|———————-|—————————————————-|——————————————————————|
| Co-op Summoning | Ember, White Sign Soapstone, optional password | Place white summon signs to invite friendly phantoms; summon by interacting with signs. |
| PvP Invasions | Red Sign Soapstone, Dried Finger, invasion items | Place red summon signs to be summoned as invader; use Dried Finger to increase invasions. |

Important Notes
– Health Increase: Be aware that summoning phantoms will typically increase the health of enemies and bosses [2].
– Post-Boss Summoning: After defeating a boss, cooperative summoning will cease except for PvP encounters [1].

This guide consolidates essential knowledge from Dark Souls 3’s game mechanics and community wisdom to help players effectively engage in both cooperative and competitive multiplayer experiences. Enjoy your time in Lothric!