The first difference is that TypeScript is open source and free to use, whereas Mascara is somewhere around the $1,000 mark per developer. You may not need to read on after this sentence, but I'll continue anyway!
Things that are similar.
Both Mascara and TypeScript expose some of the proposed ECMAScript 6 concepts early.
Things that are different.
TypeScript has more design-time tooling support. The compiler is great, but as a developer I prefer my development environment to put red-squiggly-lines under my code if I type something stupid and I like auto-completion. TypeScript does all of this (especially
if you are using Visual Studio - but other tools are getting better support too and already have things like syntax-highlighting and auto-completion).
There are subtle differences too, like TypeScript supports optional parameters and default parameters, whereas Mascara only supports default parameters (which they call "optional parameters"!). There are also some Mascara keywords that TypeScript doesn't
have an equivalent of, but you can achieve most of the concepts these keywords provide in different ways.
Personally, it's a no-brainer decision in favour of TypeScript. If there are compelling reasons to add additional language features I'm sure they will make it into TypeScript pretty soon and there is no killer feature offered by Mascara that you couldn't
somehow achieve in TypeScript.