How to unlock Rillaboom
Getting Rillaboom means pulling the Galar banner and hitting its 4★ slot. The 4★ band takes 6.5% of all pulls and holds 211 partners, so one specific Rillaboom works out to about 0.0308% per draw. The 70-pull pity counter only applies to 5★ results, so Rillaboom has no floor of its own and no targeted pull. A duplicate Rillaboom refunds 120 coins at the 4★ rate.
Rillaboom stats and rank
Rillaboom carries 115 HP, 114 speed, a ×1.39 attack multiplier, ×1.39 physical, ×1.03 special, 90 defense and 70 special defense, 530 in total. On the three-stat percentile this is 81.2 out of 100, which puts Rillaboom at rank 66 of 966 and in tier S. What separates it from its neighbours is shape, not size: its strongest slot is physical multiplier (92nd percentile) and its weakest is special multiplier (40th percentile), so it is a specialist rather than an all-rounder.
Best moves in Rillaboom's pool
At move level 5 the pool is led by Body Slam at 75.6 damage per 0.71s (147.5 effective DPS, ×1.39 multiplier), then Petal Blizzard at 33.6 damage per 0.26s (133.2 effective DPS, ×1.03 multiplier), then Tackle at 33.6 damage per 0.38s (124.5 effective DPS, ×1.39 multiplier). 8 of its 14 damaging moves scale with the physical multiplier and 6 with the special one, alongside 4 support moves. Its physical multiplier is the higher of the two (×1.39 against ×1.03), so physical moves convert better. The top option beats the second by 14.2 DPS, which decides slot one and leaves slot two as a judgement call.
Evolution cards for Rillaboom
Its starting move, Vine Whip, evolves into Power Whip once the move is at level 5 and you hold the Power card, which boosts attack for that run. If Power never appears in that run's level-up offers, the move stays at level 5 and unevolved. 14 of its 18 moves carry an evolution card, across 6 distinct cards (Vigor, Sprint, Power, Reflexes, Armor and Synthesis). The strongest of them is Body Slam at 147.5 effective DPS, so that is the one worth holding a card for first.
Rillaboom compared to similar partners
The two closest stat lines in the roster are Braviary (+0 HP, -2 speed, -0.01 attack, -20 total) and Revavroom (-9 HP, +2 speed, -0.04 attack, -30 total). Against Braviary, Rillaboom is 2 speed faster and Rillaboom hits harder by ×0.01, and the rank gap is 15 places. Those differences are what you actually trade when swapping partners, not a straight upgrade path, so neither side is a strict upgrade and the move pools have to break the tie.