You can't cast Essence Capture without a target creature spell. If either target is illegal when Essence Capture tries to resolve, the other is still affected as appropriate.
25-01-2019
wotc
A creature spell that can't be countered is a legal target for Essence Capture. The spell won't be countered when Essence Capture resolves, but you'll still put a +1/+1 counter on the target creature.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.