With minimal planning, you are able to get 2-3 weapon fusions by round 14 when you face the last round of bosses and should be able to melt them in under 5 seconds. With proper planning and some luck, you may be able to get 4 weapon fusions by minute 15

Devil's Fork: Pitchfork + Yoyo

Dimensional Slash: Tongue Lash + Katana

Fairy Tango: Fairy Dance + Yoyo

Meteor Hammer: Bonk Hammer + Toad Oil

Mole Hat: Mole Turret + Crow Boom

Shovel: Wood Axe + Mole Turret

Sweeping Slash: Twin Scythes + Weed Wacker

Tadpole Burst: Tadpole Spew + Boomerang

Tidal Wave: Water Beam + Bonk Hammer

Wind Bombs: Bombs + Toad Oil

Haybale, Lawn Mower and Bouncy Ball do not have weapon fusions

while I haven't done any real DPS testing, it feels like using any 2+ combination of Dimensional Slash, Meteor Hammer, Sweeping Slash, and Wind Bombs would easily get the achievement to pop

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