It would have to be May in RSE, not getting to fight your rival's starter @ fully evolved :/. Then there's really no competition in terms of rivals, the only other guy is wally but I guess his last battle is cool and all.
Silver in HGSS is also quite dissapointing
All the team rocket HGSS bosses<
Ghetsis' Hydreigon surely gave most a run for their money. One of the good endgame bosses. Illegal leveled fully evolveds are common with npcs and it's not like you can't do the same through emerald pomeg glitch. No big deal
Competitive Pokemon needs a "santa clause" banning the overpowered Delibird from ALL tiers ^.^