Colossus or Sky Colossus is one of the main types of sky encounters along with Relics Islands, Monster Islands, Player's airhsips, Space Rift and Sky Mazes.
Colossus (Colossi ?) invariably show up on every exploration level that is a multiple of 30.
Combat
Colossus are fought much like you fight the Monster Islands and Player's airships. You can assault them directly or go through the details page to see their stats and fight with the help of an Exploration Runestone if you so wish.
If you own Hovering and your Energy is high enough relative to the Colossus energy, you can also get an instant victory by choosing the Destroy option.
Besides spending a Runestone, other things can be helpful specifically against Colossus:
- Various Celestial Titles
Combat Stats
Colossus' parameters are 
15 
10 
5 
5 /
120.
The monster's actual stats on any given level are obtained by injecting those parameters into the same formulas used for Monster Island Enemies, see formulas here.
Colossus has a single combo skill:
- Heart of Titan:
- Replaces attack (average chance)
- Deals 120% of Main cannon's damage
- Fire +30 for the remainder of the fight
Rewards
Colossus will drop Relic Fragments, Mysterious Statues and can drop Airship fragments and most importantly the Energy Crystals needed to upgrade your Sky Medals and build Gumball Statues. See Energy Crystal to see which Crystal can be found at which level
Various effects can increase the rewards:
- Elemental Continent Halo : Sky EP + -/-/15/20/25/30% when attacking Sky Colossus
- Elemental Torrent, Magic Cannon from Elemental Continent: 10/20/30/40/50/60 Sky EP after you win the Sky Colossus battle
- Medal of Scholar in your Ancient Mining Pit : Crystal drop chance +10%/../50%
Display
An "alpha" colossus (Colossus encountered a the lowest level possible for him)
A "beta" colossus (Colossus encountered a the second lowest level possible for him)
Any Colossus as it appears on the minimap