Professor's Warning
Instant
Choose one —
• Put a +1/+1 counter on target creature.
• Target creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)
- CMC
- 1
- Mana cost
- Color identity
- B
- Rarity
- common
- Set
- Strixhaven: School of Mages
- Price
- $0.30
- EDHREC rank
- #8682
Professor's Warning is a one-mana instant that gives a creature indestructible until end of turn — it stops removal cold and, more usefully, lets you crash into a board wipe with a creature you planned to keep. The real reason to run it is that it puts a -1/-1 counter on the protected creature, which is the interaction that makes it a staple in Sarulf, Realm Eater decks rather than a generic upgrade.
Best Commanders
Commanders with the highest synergy
Sarulf, Realm Eater
Sarulf, Realm Eater grows by eating -1/-1 counters placed on permanents you control, so Professor's Warning is doing double duty: it shields Sarulf from a kill spell while simultaneously feeding him a counter and accelerating the board-wipe threshold.
Shirei, Shizo's Caretaker
Shirei, Shizo's Caretaker cares about creatures with power 1 or less dying and returning them at end of turn, so Professor's Warning slots in as a way to manufacture a -1/-1 counter that can temporarily reduce a creature's power — letting Shirei recur something that would otherwise be out of range.
Format Analysis
Where it lives, where it can’t
| Format | Verdict |
|---|---|
| commander | legal |
| legacy | legal |
| modern | legal |
| pioneer | legal |
| standard | not legal |
| vintage | legal |
| pauper | legal |
| oathbreaker | legal |
In Commander, Professor's Warning earns its slot exclusively in decks that benefit from -1/-1 counters — outside that niche, Swiftfoot Boots or Heroic Intervention protect more broadly for comparable or lower investment. In Pauper it competes with a deep pool of one-mana protection spells and the counter clause rarely matters, so it sits near the bottom of that pile. Legacy, Vintage, and Modern have access to more efficient interaction at every point on the curve, meaning Professor's Warning only shows up in deliberate counter-synergy shells rather than as a general-purpose protection spell. Across formats, the card's ceiling is defined entirely by how much work that -1/-1 counter does in your deck.
Key Combos
Combo lines featuring this card
Price Context
Current price
$0.30 bulk tier
At $0.30, Professor's Warning is bulk — easy to pick up as a throw-in or from a commons box. Bulk rares and uncommons with narrow applications rarely climb unless a new commander creates a sudden demand spike, so treat it as a cheap role-player you grab when you need it, not a card to stock.
Explore
Sources
Mentioned
- Sarulf, Realm Eater
- Shirei, Shizo's Caretaker
Updated . Data from Scryfall, EDHREC, and Commander Spellbook.