You tell Twilight Sparkle that you'd like to keep your runestones for emergency situations. You ask her about spells that can dispatch multiple foes at once, and mention an explosion spell.

Twilight Sparkle: "Well! Exploding runestones would be a little too dangerous, don't you think? Instead, how about a Shackles spell? All you have to do is kick the stone at your foes, and it should magically chain them together, stopping them right in their tracks."

You say that you like it, and that for the second one, you were thinking about a more defensive spell, or a healing spell, just in case.

Twilight Sparkle: "Most of those require channelling, which is not something runestones can do. Personally, I recommend a Homecoming spell, which can teleport you from anywhere in the world to your home, along with anyone else physically touching you."

You admit that it does sound useful, and ask how much would it cost to get those two inscriptions.

Twilight Sparkle: "Oh, don't worry about that. I trust you won't be using them to cause any trouble?"

You promise her that you won't, and offer your runestones to Twilight Sparkle. She uses her unicorn magic to inscribe them, and once she is done, the runestones begin to glow.

Twilight Sparkle inscribes your 2 Blank Runestones with Homecoming, and Shackles.

Twilight Sparkle: "All done!"