Does Double strike work with Lifelink for double the life gain?

Yes. The creature deals damage twice, and Lifelink triggers on each instance, so you gain life for both the first-strike and regular combat damage.

If a Double strike creature has Deathtouch, can it kill two creatures?

Yes. In the first-strike step it can deal lethal Deathtouch damage to one blocker, and in the regular step it can damage another, potentially destroying multiple creatures.

What is the best Double strike card?

By popularity, Lizard Blades is among the most-played Double strike cards — see the full ranked list above.

Best Double strike cards in MTG

Double strike: A creature with Double strike deals combat damage during both the first-strike and the regular combat damage steps.

Double strike effectively doubles a creature's combat damage, making it devastating with Lifelink, Deathtouch, Trample, or any power-boosting effect. Even a small Double strike creature with a pump spell can deal enormous damage, and with Trample the excess from both hits tramples over. It is a premium ability for finishing games quickly.

FAQ

Does Double strike work with Lifelink for double the life gain?: Yes. The creature deals damage twice, and Lifelink triggers on each instance, so you gain life for both the first-strike and regular combat damage.
If a Double strike creature has Deathtouch, can it kill two creatures?: Yes. In the first-strike step it can deal lethal Deathtouch damage to one blocker, and in the regular step it can damage another, potentially destroying multiple creatures.
What is the best Double strike card?: By popularity, Lizard Blades is among the most-played Double strike cards — see the full ranked list above.