- This stage has no official name.
Eldritch Forces Invasion is a special stage that appears in ★★★★ Laboratory of Relics after clearing all Stories of Legend sub-chapters on all star difficulties, much like a Zombie Outbreak or Filibuster Invasion. Upon completion, Eldritch Forces will be back to normal and Idi:N will be unlocked. This is a No Continues like the uninvaded stage, so using Cat Food to continue is not allowed.
- The boss, Idi:Re spawns at 13.3 seconds400f.
- Infinite Relic Doges spawn at 20 seconds, delay 140~143.3 seconds4200~4300f.
- Infinite Gory Blacks spawn at 43.3 seconds1300f, delay 140~143.3 seconds4200~4300f.
- Infinite Heavenly Hippoes spawn at 66.7 seconds2000f, delay 140~143.3 seconds4200~4300f.
- Infinite Relic Doges spawn at 90 seconds, delay 140~143.3 seconds4200~4300f.
- Infinite Gory Blacks spawn at 113.3 seconds3400f, delay 140~143.3 seconds4200~4300f.
- Infinite Heavenly Hippoes spawn at 136.7 seconds4100f, delay 140~143.3 seconds4200~4300f.
- Infinite Imperator Saels spawn at 160 seconds, delay 80~83.3 seconds2400~2500f.
- On base hit, 3 Imperator Saels spawn, delay 6.7~10 seconds200~300f.
Do not focus on variety, instead, bring as many combos as you can and the few cats that will allow you to win. Master Uril is strongly recommended, while any approach that relies on tanking Idi or weakening it is doomed to fail.
Lineup: various basic combos (attack, worker, research, defence etc.), Cameraman Cat, Ramen Cat, Slime Cat, two more cats of your choice (at least another meatshield unless using research combos). Use the Thunderbolt Cannon. Rich cat is also highly recommenced as there are very few money sources.
Battle: start by summoning the fastest unit you have and start spamming Ramen. You should quickly have a solid line of defence, so add Cameramen too and upgrade the worker to level 3. From now on, the fight should be almost a stalemate, but the enemies will push every once in a while, so you need to use Slime, by either spamming him or timing him, to cause some of his powerful waves against the enemy peons. You should also use the Thunderbolt to freeze Idi and give Slime the chance to deliver a free hit. If the last unit is Uril or talented Rodeo, use them only when Idi is in the half of the battlefield closer to the Cat Base. It may take a couple of attempts to get used to the timings, but, unless the units are underlevelled (which should be impossible, considering the requirements to reach this stage) or the last unit picked is a useless one, like Modern Cat, this stage should go down relatively easily.
- This is the only Stories of Legend stage to feature Relic Enemies.
- This stage has a unique background.
- This is the only stage that drops a Legend Cat that has a restriction (Only Special and Rare units).
- This is the fourth stage to have a special feature in its stage select box, this having a space-like background, the first being the Zombie Outbreaks, the second being PPAP with a special font and the third being the Filibuster Invasion with a similar space themed background.