Prism Ring

The choose-on-entry clause is the whole design. Older color-pinned lifegainers keyed off damage prevention or specific events; this one taxes nothing. Pick a color as it resolves, then keep casting that color, and the life trickles in passively. That makes the card a one-mana commitment to a single pillar of your deck rather than a reactive answer, so its yield scales directly with how mono-focused your spell base already is. A deck splashing four colors gets almost nothing; a deck pouring out one color all game turns this into a steady stream of incidental life, each spell stacking another point onto the buffer. That is the entire calculus. It produces no board presence, blocks nothing, and sits exposed to any artifact removal the opponent draws, so it demands that the life it returns outweigh the tempo cost of spending a turn-one mana on a permanent that only starts paying once you begin casting the chosen color. As incidental lifegain it belongs to the family of color-locked enablers built to buy time against fast clocks: not a build-around, just a tax-free incremental that rewards a deck already shaped to feed it.