earclacks but jank and a bootleg If you wish to do anything special beyond basic value changes you'll need to understand the template and have a bit of coding skill. feel free to ask questions (can't promise i'll reply quickly, though)
made this as a template for myself (or anyone who wishes) to create simple battle sims, when i get bored I'd create some matchups and make custom characters with different abilities fight eachother, then stream it to my friends offsite. May post the custom characters i've made later inspired primarily by horserace sim, i'd first made a prototype of this just before i knew about earclacks but it's been a bit of an inspiration since then.