Pokemon’s Hack checks suck. They are terrible. They don’t check poke balls, Shinyness, IVs, OT, EVs. (for illegal stuff). I was able to use a Shiny Groudon in a quick ball because it was registered as caught in old Hoenn. It’s Ivs we’re also modified.
They do check location met, level met. Legal moves.
Most importantly, the PID, so for example, if a Pokémon with a event move and 31x6 IVS and nature was hacked to have a PID that matches that of the Pokémon from that species (but had the event location met, level met, Cherish ball) it should be fine.
That’s about all.
By the way, I highly encourage you hack your competitive teams. Just use possible move sets and shinyness and poke ball and a correct PID.
Warning: Useless info
The best hack checking in Pokémon is when transferring between Black 2 or White 2 to Pokebank. But even then, if it’s mostly legal, pokebank re-assigns it a new legal PID.
The worst hack checking that I personally found was Gen 4 to 5.
Warning: Useless info ends here.
Summary: I give Pokémon tournament hack checks 4/10.