Will I get champion also if I'll forge mecha kingdom skin?

No. The Mecha Kingdoms tokens can be used to unlock a chroma for the Mecha Kingdoms skins. You need to purchase the champion and the skin in order to use the chroma.

Edit: The only exception to this are the Prestige skins that do not require the non-prestige version, .. but those are purchased with Prestige Points, so I assumed you aren't talking about those

The thing is, you can't get the skin for tokens

Will you get the champion? No, you won't even get the skin, all you'll get is a paint job for the skin if you ever get it