I'm glitch hunting this game and will post my findings here.
More kisses
You can produce more hearts by switching direction quickly.
Reverse jump
Barney can do a backwards jump by pressing a button and away from the raft/cliff at the same frame.
Grounded jump
Press a button and Down when near a raft/cliff. You have directional influence during the jump.
Kill yourself
By using the grounded jump, you can direct yourself into the depth. The game usually respawns you in a position where you last had ground beneath you.
Walk on rainbow slide
In music town, when sliding on a rainbow slide, you can press a button to kiss at the end in order to stop your momentum. This will cause you to stay on the slide and you can walk back up on it.
Kiss glitches
When the raft is nearby and you press Down to jump on it, Barney may produce a heart before the jump.
When walking into the goal, you can press a button on a specific frame to kiss during the victory dance.
When kissing right when starting to slide on a rainbow slide, you will produce a heart after finishing sliding.
