If you are looking for a legitimate and halal cryptocurrency with upside potential, here are the shortlisted options:

1. Cardano (ADA): A sustainable and decentralized blockchain project that supports education and health.

2. Stellar (XLM): Facilitating global money transfers in a legitimate way.

3. Polygon (MATIC): Improving the performance of the Ethereum network at a low cost.

4. Avalanche (AVAX): Supporting high-speed decentralized applications.

5. Algorand (ALGO): Advanced technology that supports smart contracts and ethical projects.

Tip: Choose a solid project, stay away from random speculation, and consult with Islamic economics experts to ensure legitimacy.