I was cruising through the Mythical Plus level dungeon when on floor 8, a weird invade of three creatures, elements Water, Fire, and Dark invaded. I couldn't find any info about them, so I hit them as hard as I could. They had high defense, so I used Shiva's active the next turn before they could attack. STILL didn't break through despite a very high multiplier and 17+ combos. Then they one-shotted me from full. What the heck are these things and where can I find info about them?