In here, post "LF: Battle with [Digimon you have and [Level]]", and state whatever optional rules that you may want to use. (LF: = Looking For)
If you would like to take someone's challenge quote them and confirm term, or negotiate terms.
[b]LF:[/b] Battle with (Digimon) [Level]
[b]Rules:[/b]
[b]Rules:[/b]
E.g.
LF: Battle with Garurumon [C]!
LF: Winner Takes All Battle with WarGreymon [M]!