Are there any Magic cards which test for first strike? I’m thinking of something like “Destroy target creature with first strike” or “Creatures with first strike get +1/+1 until end of turn”.
Four cards specifically check for first strike:
- Kwende, Pride of Femeref has "Creatures you control with first strike have double strike."
- Tresserhorn Skyknight has "Prevent all damage that would be dealt to Tresserhorn Skyknight by creatures with first strike."
- Path of Mettle has
When Path of Mettle enters the battlefield, it deals 1 damage to each creature that doesn’t have first strike, double strike, vigilance, or haste.
Whenever you attack with at least two creatures that have first strike, double strike, vigilance, and/or haste, transform Path of Mettle.
- Momentum Rumbler has
Whenever Momentum Rumbler attacks, if it doesn’t have first strike, put a first strike counter on it.
Whenever Momentum Rumbler attacks, if it has first strike, it gains double strike until end of turn.
A several cards gain or grant a variety of keyword abilities based on the abilities other creatures or creature cards have, including first strike:
- Akroma, Vision of Ixidor
- Cairn Wanderer
- Concerted Effort
- Escaped Shapeshifter
- Kathril, Aspect Warper
- Majestic Myriarch
- Odric, Lunarch Marshal
- Thunderous Orator
Several cards exile or otherwise remove cards, and then gain a variety of keyword abilities that those cards have:
- Animus of Predation
- Death-Mask Duplicant
- Eater of Virtue
- Rayami, First of the Fallen
- Urborg Scavengers
I found these using the Scryfall searches
o:/if.*has.*first strike/, and
o:/as long as.*has.*first strike/. You could replace "first strike" with other keyword abilities in those searches to find cards that care about those keyword abilities.
Try this search: https://scryfall.com/search?q=o%3A%22with+first+strike%22
Here are two cards that meet your criteria: