Ash lost in the 4th gen league to a legendary trainer who had a full team of 6 legendary pokemon on him. It took Ash 5 of his pokemon to even beat the 1st legendary pokemon, Darkrai (Sceptile was the one to take him out btw), and finally his last pokemon, Pikachu to take out the legendary trainer's 2nd legendary pokemon, Latios. Unfortunately it was a double KO, so Ash lost, and the legendary trainer still had 4 legendary pokemon left on his team. Ash ended the Sinnoh League in the Top 4.