Add asymmetric temporal enemies to Temporal Crucible encounter

[Copilot]

Refines the temporal arena encounter with enemies that exhibit opposite vulnerability patterns across timelines, creating a strategic puzzle where players must attack one enemy early and avoid another until late.

New Enemies

Chrono-Spawn - Growing threat (weak → invulnerable)

• Past: Takes double damage, AC 12, weak attacks
• Present: Standard stats
• Future: Resistance to all damage, 10 HP/round regeneration, frightful presence

Echo Revenant - Fading spirit (invulnerable → vulnerable)

• Past: Immune to all damage, intangible, repositions only
• Present: Resistance to physical damage, gains attacks
• Future: No resistances/immunities, full power

Strategic Puzzle

Players face opposing pressures:

• Kill Chrono-Spawn in Past (before it becomes unkillable)
• Ignore Echo Revenant in Past (wastes actions on immune target)
• Wait for Future timeline to kill Echo Revenant when vulnerable

Supporting Changes

• Asymmetric Temporal Puzzle section: Explains core dilemma, strategic tension, victory conditions
• Enemy tactics: Other enemies protect vulnerable Chrono-Spawn; Echo Revenant baits wasted attacks
• Crowd Favor hooks: +4 for early Chrono-Spawn kill, +2 for recognizing Echo Revenant trap, +3 for patient Echo Revenant kill
• Announcer beats: Evolution commentary, futility warnings, patience rewards
• GM tips: Visual tracking (progressive token sizes, transparency), immunity reminders, strategic hints

Flex scaling: Add one asymmetric enemy for 5-6 PCs, both for 6+ PCs.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Refine temporal idea</issue_title>
<issue_description>I really like the temporal idea where there are three different time periods they had transported back and forth between..

Let's play it out a little bit more where there's an enemy in the early period who becomes invulnerable or very powerful in the last period. And conversely, we need to create an enemy who's invulnerable in the first period but is vulnerable in the final. The players have to avoid one and attack the other based on time period.

Brainstorm some ideas with this symmetry in mind. </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Refine temporal idea #85

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