Gather 3 Pollen from magma blooms. Big red leafy plants. You can pick these up while you are looking for the magmatic destroyers (see next step), as you will most likely see lots of blooms while looking for those mobs.(Not all spawn locations for destroyers have the blooms). There is a batch near the loc ( -1304.06, 211.17, 293.32 ) /waypoint -1304.06, 211.17, 293.32.
Kill 2 magmatic destroyers. These pop on you when you walk around the edge of a lava pit or lava river I got one at ( -1425, 209, 263 ) /waypoint -1425, 209, 263 and another at ( -1512, 209, 435 ) /waypoint -1512, 209, 435. Note that if you do not kill it on the first pop, it will return to the lava, and will not pop again for 10 minutes or so. One of mine was an 83^ the other an 80^.