His field effect, the Corrosive Field, damages every Pokémon that switches in with type-scaling Poison-type damage (so it's basically a Poison-type Stealth Rock that can't be removed). It gets even worse in Pokémon Reborn Hardcore, in which ZEL gets a Jolteon (which pretty much always moves first at this point in the game) and Taka gets his Gligar and Klefki from his first battle with you. ZEL is no slouch, either they have a Glaceon (which is very bulky and can hit very, very hard), an Espeon (which is rather frail but is very fast and powerful), and an Umbreon (which is bulky as heck and has tons of status-inducing moves). If this wasn't bad enough, most of their Pokémon are a pain: while Taka's Lileep (Exeggcute in later versions) is pretty easy to handle, his PULSE Tangrowth hits like a truck and has incredible defenses, while his Chatot has great speed and can wipe entire teams if it sets up a Nasty Plot. To start with, you have to fight them in a double battle.