Most pages answering this question either wave it away ("nothing ever happens") or terrify you for clicks. The truth is in between and depends on what you do, not whether you mod. Here's the honest breakdown — not legal advice, but a realistic picture of the law and its enforcement.
Creating a modded APK means copying and altering copyrighted software, and distributing one means distributing an unauthorized derivative work — infringement in essentially every jurisdiction with copyright law. That part isn't gray. Using one privately occupies a grayer space: in most countries, personal use of an infringing copy isn't itself a criminal offense, and civil claims against individual players are rare to nonexistent.
Separately from copyright, using a mod violates the game's terms of service — a contract matter, not a criminal one. The remedy for that is account suspension, not court. It's worth keeping the two ideas apart: ToS violations get accounts banned; copyright infringement is the developer's legal claim against distributors.
Enforcement against individual players for using a mod is essentially unheard of. What developers pursue, in practice, is: sites that distribute mods at scale (takedowns, sometimes lawsuits), paid mod sellers (fraud on top of infringement), and mod users who damage the game's economy or other players (via account bans under ToS, not courts).
The realistic risks for a player are therefore practical, not legal: losing an account, losing local saves, or installing malware from a bad source. Nobody is suing someone for installing a modded Puzzle game.
Mod on your own device, on accounts that aren't precious to you, in games where other players aren't affected. Scan every file before installing. Never pay for a mod. Don't redistribute. That combination — which is how most people actually mod — carries no realistic legal risk and minimal practical one. The people who get into trouble are almost always doing something beyond that: selling, distributing at scale, or wrecking games other people paid to play.
Realistically, no. Downloading for personal use isn't something developers enforce against, and in most jurisdictions it isn't criminal. Distribution and selling are entirely different matters.
Both, depending on the act: creating or distributing a mod infringes copyright; using one violates the game's terms of service. ToS violations get accounts banned; copyright is the developer's claim against distributors.
Even then the copyright usually lives on with whoever holds the estate. In practice, enforcement for personal use doesn't happen regardless — but "the company is dead" doesn't make the work public domain.