Quicksilver Elemental has at least one +1/+1 counter on it.
Quicksilver Elemental does not have summoning sickness.
({U} magic symbol) ({U} magic symbol) available.
Steps
Activate Quicksilver Elemental twice by paying ({U} magic symbol) ({U} magic symbol) , causing it to gain all activated abilities of Incubation Druid and Horseshoe Crab until end of turn.
Activate Quicksilver Elemental using Incubation Druid's first ability by tapping it, adding ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Activate Quicksilver Elemental using Horseshoe Crab's ability by paying ({U} magic symbol) , untapping it.