When comparing Polycode vs Unity 2D, the Slant community recommends Unity 2D for most people. In the question“What are the best 2D game engines?” Unity 2D is ranked 7th while Polycode is ranked 32nd. The most important reason people chose Unity 2D is:
2D game creation was a major feature request from the Unity community and was added with version 4.3. 2D is provided in both the Pro and Free distribution of Unity.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Can create portable native applications
Polycode uses Lua and C++ to create native applications for Windows, Mac, and Linux. Mobile platforms are planned for the future.
Pro Free and open source
Polycode is free and open source (released under the MIT license). The source code is freely available on GitHub.
Pro IDE for 3D editing
Recently, the editor and its integrated tools have been released in compiled form. Features coding and scene editing in one application.
Pro C++/Lua
Polycode is distributed in a C++ form as well as with IDE. And there's an additional LUA-based scripting system.
Pro Built into Unity 4.3+
2D game creation was a major feature request from the Unity community and was added with version 4.3. 2D is provided in both the Pro and Free distribution of Unity.
Pro Integrates with Mecanim
Mecanim brings state machines and blending to 2D bone animation. The state machine editor allows for designers and programmers to visually create a Finite State Machine (FSM) to control when animations should play. Mecanim also allows for blending so an animation can transition smoothly between two states without the need of in between frames made by an animator.
Pro Sprite Sheet and Bone based animation supported
Both types of 2D animation for game development are supported in Unity’s system and can be used interchangeably in the timeline.
Pro Easily change sprites dynamically
Usually used for character customization, programmers can change any sprite in a bone animation at runtime easily by referencing the bone and loading the new sprite from the resources folder.
Cons
Con Abandoned
The project does not seem to be maintained anymore: there has been no new release nor commit since mid-2015.
Con No mobile support
Doesn't have support for Android or iOS.
Con Lacks critical features
- Vertices can't be animated, so you can't have ANY organic feel (like... lungs breathing).
- Parent bone can't be animated without affecting the children. This is especially impeding for organic feel, again.
- No option to show & unshow assets (or it is hidden), like for switching weapon on your character for exemple.

Con Poor script interface for texture atlases
Accessing individual sprites within an atlas texture is possible at runtime, but requires use of the Resources folder subsystem.
