If you're new you don't have access to the characters that can destroy his tiles. There are several 2 and 3* characters that can either destroy or reverse them. Ms. Marvel's red blast is probably the first you'll encounter.
Until you find that, all you can do is avoid matching purple and try to survive until your heroes can use powers. His defense tiles are relatively weak at low levels, so Iron Man's Unibeam will cut right through it. Once you drop him you can clean up his tiles and regain normal damage.
You can also get rid of them with a 4-tile row sweep, when its available. New ones only appear if you match purple tiles, not if you destroy the old ones indirectly.