My method to overcoming the leech/ingrain glitch was multiple attemps (by multiple I mean tens of) and using minimon that have the elemental advantage. The early badge was easy, but getting the Grass badge involved me doing a crazy number of attempts and playing a chess game against the leader by figuring out the pattern in which they deploy minimon.
Anticipate the leaders minimon switch.
My method: Start with Bouldon, switch to ravenoss, switch to mosseye, switch to ravenooss (this will be the first time you attack, use wingwhatever and 1 his the deesmus lil head guy) switch to mosseye (soak up a rockwall move from bighead minimon) switch to rovenoss use pursuit, switch to mosseye, switch to ravenous use pursuit, switch to mosseye, switch to ravenous use pursuit, kill the big headminimon, switch to bouldon (ballike evolved form will immediately be switched out), switch to ravenoss 1 hit the scarecrow guy, switch to bouldon, (gym leader hass balllikeevolved formguy and will use endure out of fear I guess), 1 hit ballsilkwhatever with arm thrust, switch to ravenoss 1 hit the horntusk final mob. Win.
This took me like 35 attempts to get the pattern, but 3 to perfect it and win. Its all about switching 1 step ahead of the gym leader and using the right minimon to get 1 hit KO's without ingrain or leech seed being used. Still, the game can glitch out.
And thats how you become a minimon master yo.