Buu simply extends his head tentacle and uses it to whip or constrict the opponent.
Super Buu uses this technique against Super Saiyan Gotenks during their battle in the Hyperbolic Time Chamber, wrapping his leg and slamming him against the ground several times. A little later, Super Buu (w/ Gotenks absorbed) uses the technique against Gohan as part of his Bring It! rush attack. Then, as himself again (without the Z Fighters absorbed), Super Buu uses the attack on Goku twice when inside himself.
Video Game Appearances
Elastic Tentacle is one of Super Buu's special moves in Dragon Ball Z: Ultimate Battle 22.