Just a cheer while warming up for a game:
One player: My name is [insert name here] and I know what I got!
Rest of the Team: What do you got?!
OP: I got a team that's hotter than hot!
RT: How hot is hot?!
OP: Not even batman or superman...
RT: Uh-huh, uh-huh!
OP: ...can do what my team can!
RT: SO KEEP THAT FAITH!
Here's another:
OP: Way down in the cemetary!
RT: (Way down in the cemetary!)
OP: That's where your team's gonna be buried!
RT: (That's where your team's gonna be buried!)
OP: Six feet down and seven feet under!
RT: (Six feet down and seven feet under!)
OP: WHEN WE YELL WE YELL LIKE THUNDER!
RT: (WHEN WE YELL WE YELL LIKE THUNDER!)
OP: (Spell out mascot's name)
Something the players can do during the game after they did something good is a power clap. To do this one player yells, "Power clap on three! One, two, three..." and then everyone one on the team claps once as hard as they can. It's pretty cool.
As for the ace cheer, you can make a sequence of moves and then yell ace at the end. An example: clap in front of you, clap in back of you, clap in front of you, clap underneath your leg, clap in front of you, then point to the ceiling and yell "Ace!" Make this a quick sequence. It's fun! Haha.
For the encouragement of the players on the court during a game, the players not in the game at the moment can yell, "S-I! S-I-D! S-I-D-E-O-U-T! Sideout!" *clap clap* "[mascot's name]!" *clap clap* "Sideout!" *clap clap* "[mascot's name]!" *clap clap*. Just don't yell this at the wrong time (in the middle of a play, while the other team is serving, etc.), because it can really tick the other team off - I know from personal experience.