Hypercooled nanofusers can generate two doom whips from the same source, doubling bloonicide
~ Official description
Double Doom Whips

Double Doom is the final non-epic arm upgrade on the Tech path. It makes its debut in Bloons Super Monkey 2 and costs Blop Cash Icon15600. Like all Tech path upgrades, it cannot pop Glass Bloons without Research. Double Doom includes 2 Doom Whips on each arm, though one looks like a Pulse Whip.