Can Here to Help reduce the cost of Master Yi Unstoppable alongside the reduction from XP Level?

Yes, Here to Help can reduce the cost of Master Yi, Unstoppable in addition to the cost reductions provided by his Level ability.

According to Rule 356.4, multiple cost-reduction effects are applied to the total cost of a spell or unit play. Since both Here to Help and Master Yi, Unstoppable's Level ability apply to the cost of playing the unit, you sum these discounts together.

How it works:

1. Level Reduction: When you play Master Yi, Unstoppable, his cost is reduced based on your current XP level (e.g., if you have 3 XP, he costs [2] and [1] Power less).
2. Here to Help Reduction: Here to Help provides a separate, flat reduction of [3] to the unit's cost.
3. Final Cost: Both discounts are applied to the card's base cost (12 Energy, 3 Power). As long as the resulting cost does not drop below 0 (per Rule 356.5), the total discount is the sum of both the Level reduction and the 3 Energy reduction from Here to Help.

This is a standard interaction where independent sources of discounts stack to reduce the final cost of a card.