Lean, mean fighting machines can classify some of the bosses in Chrono Trigger, but all of them can be classified as tough.  HP counts are approximated because Lucca's Sightscope can't read bosses.  Besides a picture of the boss and recommended team to face it, you can find out its location, time period, HP, Main attacks, Major Weaknesses, and a mini guide for handling the boss.
Boss Name: Giga Gaia
Recommended Team: Crono, Ayla, and Robo
Time Period/Location: 12,000 BC/Mountain of Woe
Hit Points: Hands- 2000 HP, Body- 9500 HP
EXP/Tech Points/Gold: 3000/30/3000
Main Attacks: Red Flare Attack, Shadow Attack, Grab party member, Cure, Revive Hands
Major Weaknesses: Techs that can attack more than one portion
Mini Guide: Giga Gaia is a very powerful boss until you can get rid of at least one of his hands.  His hands can double team to cast Shadow and Fire damage, and one of the hands will heal the main torso of Giga Gaia.  Use spells that can damage both hands like Luminaire, Lightning 2, Laser Spin, etc until you get rid of the hands.  Giga Gaia will revive the hands, but until he does, hit him as hard as you can.  Repeat the process of eliminating the hands and hammering the body until you get rid of the monster guarding the Guru. 
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Characters-    #1           #2           #3
Characters-    #1            #2         #3
Characters-    #1           #2        #3
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