Discord.js v12 Inline Replies w/ Default Mention Settings

ExtendedMessage.js

const { APIMessage, Structures } = require("discord.js");

class ExtAPIMessage extends APIMessage {
    resolveData() {
        if (this.data) return this;
        super.resolveData();
        if ((this.options.allowedMentions || {}).repliedUser !== undefined) {
            if (this.data.allowed_mentions === undefined) this.data.allowed_mentions = {};
            Object.assign(this.data.allowed_mentions, { replied_user: this.options.allowedMentions.repliedUser });
            delete this.options.allowedMentions.repliedUser;
        } else {
	    // Changing replied_user to true will turn mentions on by default
	    this.data.allowed_mentions = { replied_user: false }
	}
        if (this.options.replyTo !== undefined) {
            Object.assign(this.data, { message_reference: { message_id: this.options.replyTo.id } });
        }
        return this;
    }
}

class Message extends Structures.get("Message") {
    inlineReply(content, options) {
        return this.channel.send(ExtAPIMessage.create(this, content, options, { replyTo: this }).resolveData());
    }

    edit(content, options) {
        return super.edit(ExtAPIMessage.create(this, content, options).resolveData());
    }
}

Structures.extend("Message", () => Message);

index.js

const { Client } = require("discord.js");

require("./ExtendedMessage");

const client = new Client();

client.on("message", msg => {
    if (msg.author.bot) return;
    if (msg.content === "hi") {
        msg.inlineReply("hello");
    }
});

client.login("ur token");

If you want to change whether the author is pinged by DEFAULT change the 'false' on line 13 to 'true'