Defend the Celestus

Instant-speed counter distribution is the whole reason this earns its slot over the sorcery-speed pump spells it otherwise resembles. Three +1/+1 counters is a fixed quantity, but the flexibility lives in the spread: dump all three onto one attacker to push past a blocker or over a lethal threshold, or fan them across two or three creatures to develop a wider board. Because the counters are permanent, this doubles as combat trick and long-game investment: cast it in response to a block to blow out the math, or cast it main-phase to bank stats that survive the turn. That permanence is what separates it from a Giant Growth effect, where the boost evaporates at end of step; here the mana buys durable board presence, and the instant timing means you never have to commit to it before you know what the opponent does. Green has a deep bench of counter-payoff creatures, and a spell that seeds three counters at flash speed slots naturally into any deck that wants to trigger "whenever a creature gets a counter" effects or feed proliferate down the line. It is a modest, honest piece of green combat math: not a bomb, but a clean answer to the problem of a green deck wanting to spread growth across a team while keeping the option to hold up mana.