Magicka + SG sync account

Check the steam store page for each bundle, that's the best way to check if you have it.
For magicka and others, steamgifts doesn't see that you already have the DLCs

Some of the Magicka DLC (and some other game DLCs) aren't recognized.
If you have the Enhancement Add-On, you can choose to permanently filter out giveaways for those DLCs by clicking "Ignore" underneath their listing.
To check if you have them, you can visit each of their pages on Steam while logged in on the Steam web site. Or, as a timesaver, go to the main game page, click See All underneath the DLC listings, and click ADD ALL DLC TO CART. Then, in the cart, it will show you which ones you already own (you have to manually remove them from the cart one-by-one, unfortunately).

you won magicka collection, in that bundle you get the game and a lot of DLC

You can either check the individual store pages for these DLC and Steam will tell you if you own the or not. Another thing you can do is right-click on the game in your library and select "Show Downloadable Content". It will give you a list of all the DLC you have installed.

If you've got the SG enhancement add-on script you can also set those to be ignored next time you see them.