When I first tried the Colossal mascara, I wasn't looking for much (I just wanted a waterproof mascara). So I was pleasantly surprised when it naturally lengthened my lashes and didn't clump up at all. This mascara features quite a big brush which does get annoying when trying to apply it on your lower lashes. It thickened my lashes and lengthened them slightly. A second coat is necessary if you're looking for a more dramatic look. However, it tends to clump your lashes up when you apply a second coat. For people who prefer much more dramatic looking lashes, this might not be the one for you. Lasting wise, I never find any of Maybelline's waterproof mascara's smudging on me. It definitely lasted for the whole day for me (it didn't even run off when I took a shower!!)
Overall, it's nice but doesn't do much compared to other drugstore mascaras.
As for the Magnum, it features a thinner and slightly curved brush, which I think helps curl the lashes. I can apply this without curling my lashes beforehand and it still gives me nice and perky lashes. It lengthens and thickens beautifully which I absolutely LOVE. What's better is that it doesn't clump on me even on the second coat. The first coat gives you natural looking, but long lashes. For a more dramatic effect, applying a second coat definitely helps. However, I would stop there because a third coat seems to be pushing it and it doesn't do much (other than making you look like you only have three lashes).
I definitely prefer this over the Colossal, but the two applied together gives me the perfect effect since one is more volumising than the other one.
xx Tiffers :)