1)How can I get Leena,Gleen,Pierre,Doc & other character thah I have'nt..

1.To get Leena first you should go to cape hawl and fight Karsh,Solt and Peppor with Kid.She will ask you to come along with you and you refuse.Keep refusing 3 times until she go.Don't worry she will join you when you go to sneak to viper manor.Glenn and doc can be got by refusing to help kid after she is stabbed from lynx and macha will also join you{Korcha's mother}.Pierre can be got by giving him his hero medal to get him to join your party you have to talk to the kid that is running around the scarcrow and he will give you the medal.Go give it to Pierre and he will join.

2.Chrono Cross should be used to know the good ending and beat time devourer.You can end the battle after using it.To do so use a yellow element then red then green then blue then white then black then chrono cross.The elements that are used will be displayed beside the field in the northwest side of screen.
Hope I Helped.

To get leena it will be a chance to get her when your stuck as lynx. She will team up with you to help you get back your true form.( I forgot how that really worked but that is the first step on getting her.) glean will come to you later in the game. Pierre you have to recruit him before you go to viper manor at the beginning of the game. He is in the back room of the place where you get weapons. He will say somethings about a pendeant that he wants. There will be a child running outside in front of a scarcrow. Talk to the kid to get the pendant. Take it back to pierre. To acquire him. To get doc you will have to make kid give her pendant when she is sick.(after lynx stabs her back at the manor). After you get the hydra potion and the doc heals you he will be in the first room sitting in a corner. Talk to him and he will want to join you. There are list of the charactors on the internet try finding out where and you will know who you don't have.

There are two ways to kill the time devourer. One you can just defeat him. 2 there is a color code for the chrono cross to work. Such as orange red blue green black white in that order.