At its worst, it's still a 6 mana costed card with 7/6, Trample and Haste, so it's still a strong card without its ability
If heads, Machamp is not Knocked Out and its remaining HP becomes 10 instead
This is where cards like Puppet Strings, Staff of Domination, and Magewrights Stone will come in very handy, as you can use them to stick a fate counter on a creature, then blink or sacrifice it as needed
Now, such a format would need a much more extensive ban list, rather than just stating no inverted triangle security stamps. Ultimately, while many MTG players are upset with this change, its worth remembering that Magic has a massive casual audience
If heads, prevent all damage dealt to this pokemon.
"Gandora the Dragon of Destruction" from Yugi's Legendary Decks