I dropped Tangrowth for Celebi.
Its doing mean things to several teams. Team hasn't lost to anyteam, including weather since the change. However, the Calm Minding slowbro lacks Slack Off and with regenerator + lefties seems to survive long enough to make a difference.
The only real 'issue' is that I lack a physical attacker after Mamoswine dies, so this team might loose stall wars.