Research Levels are a general rating of how powerful a combined creature is. While Stats are specific aspects of this, the Research Levels are an overall representation of a creatures's strength in combat. The Levels range from 1 to 5, shown in-game as roman numerals (I, II, III, IV, V).
When a game of Impossible Creatures begins, all players are at Research Level I. To unlock stronger creatures, they must buy Level II using the Lab, costing some resources in the process. The players can then advance to Levels III, IV and V, but only in that order; one cannot simply "skip" a level.
Some structures also rely on Research Levels. For example, the Water Chamber can only be built until Level II is unlocked, and some of the Research Clinic's upgrades are Level IV. However, the Genetic Amplifier can upgrade creatures of any Research Level regardless of what Level the player is actually at.
Levels[]
I[]
All games begin at this, the most basic of all the Research Levels. Players have access, wether directly or indirectly, to most buildings at this point. Once a Creature Chamber is built, a player may create Level I creatures straight away. These creatures are the weakest in the game and do not have many abilities but can be useful to defend with while setting up a base, or even for an early rush against the opponent.
II[]
Players will have access to the Water Chamber and water-bound creatures upon reaching this level, as well as the Genetic Amplifier. Ranged creatures and abilities such as Leap Attack appear in this Level, owing for more diverse combat between opponents' armies.
III[]
Unlocking this Research Level grants access to the Air Chamber and flying creatures, presenting even more options for battle. The Poison-based abilities also appear here. This is often when battles can start to get really intense.
IV[]
Research Level 4 unlocks a few new items at the Research Clinic. Creatures of this Level are well-rounded in offense and defense or have especially high attacking power. Defile Land and Loner are also available at this point.
V[]
Level 5 creatures are the most powerful, and most expensive, in the game. Their attack power, health and defense are often very high, or it may be that their damage output is extreme. Creatures of lower Research Levels generally have little hope of standing up to them, assuming numbers are equal on both sides. Combat between Level 5 creatures is vicious and both teams can end up with serious casualties.