Glowstone Recluse

Reach on a green body is the least of what this Spider offers; the mutate cost is where the arithmetic starts. Fold it into a creature pile you already control and the mutate trigger banks two +1/+1 counters onto the resulting stack. This is exactly the kind of piece mutate was designed to reward: it draws no cards and clears no blockers, it simply makes the pile bigger and harder to attack past. The counters are the durable half of the payoff, because mutate reassigns abilities but leaves counters sitting where they landed, so a stack that runs through this card more than once keeps accumulating size even as the top permanent changes. Pair that with reach and you get a body that both climbs and walls, which is why it plays as the load-bearing floor of a mutate pile rather than its showpiece layer. The trade the mechanic asks you to accept is worth naming plainly: every card feeding the stack rides on a single permanent, so one well-timed removal spell answers all of them at once. Mutate concentrates value and risk in the same motion. What this Spider contributes to that gamble is defensive insurance (reach discourages the aerial races that punish a ground-bound pile) and raw size that persists, so if the stack survives, it survives large.