Any episode with Tutwig in it is a good episode to me!
Team Rocket's antics in the Sinnoh Underground were way more appealing to me than Ash's Gym battle with Gardenia tbh; I especially liked how TR's eyes turned into Spheres. Anyway, Gardenia's Cherubi must've been pretty durable to force Ash to switch Pokemon and I screamed when Staravia lost to Turtwig. Turtwig vs. Turtwig was enjoyable though.
I liked how, just like in the games, the writers put in the Sinno Underground.
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"If you fail to plan, you plan to fail" - Sgt. Greg Parker, SRU
The Sinnoh underground tunnel didn't look as impressive as in the games but Ash versus Gardenia round 2 was good. 8/10