After you escape from the robots in the factory, you reach the End of Time.
Explore the End of Time
Talk to the man at the lightpost.
Whenever you want to change party members, just press Y. You can change members any time you want, from anywhere and time period in the world, except during battle.
Check the sparkle on the left to heal up. Save if you want.
Then, when you try to leave, the old guy calls you back. Talk to him, and do as he says: go in the room behind him.
Talk to the monster. Then, when the time comes, do the following, THREE TIMES: walk into the left side of the door frame, then walk left against the wall, up, right, and down. Repeat two times.
If you managed to avoid a lot of fights, Spekkio will be in the form of a frog, and you have access to an additional Magic Tab if you beat him, which you would have missed if you were at a higher level.
For the frog form you'll be at a good level to fight him (he changes forms when your lead member is at level 10). All physical attacks miss, so with a party of Crono, Marle, and Lucca, just test out your newly learned magic abilities. It's not hard to win.
Remember to come back here when Crono's at level 19 to fight Spekkio's Kilwala form.
Switch your other member into your party and bring them to Spekkio. Then leave the room.
Talk to the old man again.
If you use the bucket and beat Lavos now, you get ending "Good Night"
First, take the middle pillar back to Proto Dome. Walk around in front of the Gate until you hear a sound, then pick up the Power Tab that appears.
Now, go back to the End of Time and take the top pillar to 1000 A.D.