Spida

The origin story — a Radioactive Spider (green-glowing, sparkling, 24 HP, poison-immune) spawns rarely at night across the Overworld; there's also a spawn egg and an ops-only /spiderpowers grant|revoke command. Its bite poisons and disorients you for a few seconds… then grants permanent spider powers (they survive death and relogging) plus the "With Great Power" advancement.

The powers

• Shoot web (C) — web globs damage and tangle mobs (heavy slowness + weakness) and splat cobwebs onto surfaces that self-dissolve after ~30s, so no world litter
• Web swing (hold V) — latch onto any block within 48 blocks and swing on real pendulum physics: WASD air-steering, hold jump to reel in and zip up, release at the top of the arc for a momentum launch, with a sagging web-line rendered from your hand
• Wall crawl — walk into walls to climb them, sneak to cling
• Spider agility — no fall damage while swinging or wall-catching, half otherwise