I just cast Nantuko Slicer with kicker, with a single Smogbelcher Chariot in my own graveyard, and a lone Tolarian Geyser in my opponent's graveyard. I got no prompt, nothing happened. Attached game state for reference.
Seen on Forge v.1.6.56-SNAPSHOT-04.09 Windows.
#Nantuko Slicer does nothing?
peak tusk
edgy fulcrum
[[Nantuko Slicer]]
silent reefBOT
Creature — Insect
Kicker 
When Nantuko Slicer enters the battlefield, return target card from your graveyard to your hand. If this spell was kicked, conjure a duplicate of target card in an opponent's graveyard into your hand. It perpetually gains "You may spend mana as though it were mana of any color to cast this spell."
3/2
exotic swan
Hmm just tested this and the card seems to work fine. maybe it skipped the prompt because there was only 1 valid target ?