As someone who is striving to complete such missions and hasnt been lucky enough to complete more than one of them just yet, the below list of Secret Mission conditions is provided by the folk over at Pokemon Zone
they hold meaning for team members, too
If you load up your deck with other creatures with damage-dealing abilities, this could be useful, but its definitely niche
Im sure that there are even more cool ways to use this card that Im not thinking about, giving all of the crazy things that Ive seen people put together in Commander
Now, it makes use of Snowl as a secondary boss monster, and this Deck gets more aggressive by providing up to three Noraml Summons for free
Whenever Neheb deals combat damage to a player or planeswalker, you may discard any number of cards