1-21 ALDEBARAN
1-21 Aldebaran is the 21st stage of Cosmos Ch.1 — Beyond the Exosphere. Previous stage: 1-20 Vega. Next stage: 1-22 Betelgeuse.
Shibalien Elite and Star Peng are Alien. Anti-Alien units take less damage and deal more.
GROSS CAT A Its True Form is Strong Against Alien, giving budget anti-Alien value. 
LI'L GROSS CAT B True Form has a 30% Knockback vs Alien. 
BAKERY CAT A Curses Alien enemies. 
LITTLE LEAGUER CAT S Resistant vs Alien and Long Distance — a budget anti-Alien backliner. 
THE WHITE RABBIT S Slow, Strong and Weaken vs Alien. Also fits “Counter Red.” Ginger Snache, Sir Seal and Pigge are Red. Anti-Red units take less damage and deal more.
FISH CAT A Strong Against Red and tanky for the cost — a sturdy anti-Red frontliner. 
BEAN CATS B Knockback and (True) Resist vs Red enemies. 
CARPENTER CAT A Resistant to Red — durable against Red attackers. 
APPLE CAT A Freezes Red enemies (100% in True Form). 
CAT MACHINE A Resistant to Red enemies. Also fits “Counter Alien.” Mix of Shibalien Elite + Star Peng. Anti-Alien army with Warp-Immune backliners.
First Row 1 restriction in the Ch.1 mid-game — your usable cats collapse to one row (10 slots). r/battlecats's universal advice: 'pre-build your Row 1 with the cats you actually need before queueing this cluster.' Enemy mix is moderate: Star Peng + Sir Seal (Red) + Pigge + Ginger Snache + Shibalien Elite. The challenge is constraint, not enemy difficulty. Lineup (Row 1 only): Mohawk + Manic Mohawk → Bahamut Cat → 1-2 Anti-Red Ubers (Mighty Reza, Crazed Bahamut) → Warp-Immune backliner for Star Peng. Common failure: forgetting that Row 1 is your bottom row in the lineup editor. The stage banner shows '↑ Row 1' but if your bottom row is full of Crazed cats you weren't planning to use, you ship them into the stage.
The castle you destroy to clear the stage.