Raichu PK is not really a good counter compared to the mentioned ones because once it discards all the energies, it will be useless & not to mention the low HP whereas if you play Ampharos SW, you only need to discard 1 Lightning energy & you can also snipe with its attack & Poke-Body. As for Meganium δ, its second attack can help to reduce damage & it will be better if you are playing it against Water Pokemon...