Surly Badgersaur's abilities are triggered abilities, not activated abilities. They don't allow you to discard a card whenever you want; rather, you need some other way of discarding a card, such as a cycling ability.
2020-04-17
wotc
If you discard a card as a cost to cast a spell or activate an ability, Surly Badgersaur's triggered ability resolves before that spell or ability but after you've chosen targets for it. If you discard a card while a spell or ability is resolving, that spell or ability finishes resolving before Surly Badgersaur's triggered ability does.
2020-04-17
wotc
If the target creature is an illegal target when Surly Badgersaur's last ability tries to resolve, the ability doesn't resolve. If it's a legal target but Surly Badgersaur is no longer on the battlefield when the ability resolves, the target creature won't deal or be dealt damage.
Format Legality
Standard
Not Legal
Future
Not Legal
Historic
Not Legal
Timeless
Not Legal
Gladiator
Not Legal
Pioneer
Not Legal
Modern
Not Legal
Legacy
Legal
Pauper
Not Legal
Vintage
Legal
Penny
Not Legal
Commander
Legal
Oathbreaker
Legal
Standardbrawl
Not Legal
Brawl
Not Legal
Alchemy
Not Legal
Paupercommander
Not Legal
Duel
Legal
Oldschool
Not Legal
Premodern
Not Legal
Predh
Not Legal
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