Avoid simulators that ask for downloads. The best versions run entirely in your HTML5 browser.

: The typical bullet box and turn-based combat are removed. Instead, you must dodge massive vines, flamethrowers, and "friendliness pellets" in real-time. Dynamic Difficulty

Simulators typically strive to mirror the complex, multi-phase mechanics of the original 2015 fight: omega flowey - Apps on Google Play

In the original game, the Omega Flowey fight isn't hard just to be hard. It is terrifying because you’ve just watched Flowey absorb the six human souls, murder the screen itself, and trap you in a void. The fight is broken up by static, horrific facial close-ups, and the soul-recharging segments feel like desperate pleas for help from your friends.

Fans have painstakingly rebuilt the fight within other game engines, including a massive 8,000+ command block project in and a multiplayer-optimized map in Team Fortress 2 Core Gameplay Mechanics