NTEVO ROMs are "vanilla" enhancement hacks. Unlike "difficulty hacks" or "new region hacks" that fundamentally change the story or world, NTEVO versions aim to keep the original experience as pure as possible while removing technical barriers. In these versions:

Enables solo play for the original 151, allowing Kadabra and Haunter to reach their final forms through leveling.

Additionally, some high-quality enhancement hacks like Heart and Soul build upon the NTEVO concept by adding other quality-of-life features, such as the Physical/Special split, following Pokémon, and infinite TMs, while still offering the solo-evolution fix. How to Get and Play NTEVO Games