Iron Hands:
Look here for why
Garganacl:
- Slow and Bulky, good because Tera raids have you attack out of turn.
- Rock is a good offensive type
- Not sure if Salt Cure works in raids, but if it does then its good.
Baxcalibur:
- Amazing attack stat
- Ice is also a good offensive type
- Access to Swords Dance for boosting
- Glaive Rush is a very strong STAB move.
Iron Valiant:
- Amazing Attack
- Good offensive type
- Gets Swords Dance for a boost move
- Booster Energy Quark Drive attack boost can't be removed
Gholdengo:
- Good Offensive and Defensive type
- Amazing Special Attack
- Gets Nasty Plot
- Make it Rain hits hard and the SpA drop can be helped by Nasty Plot
Great Tusk:
- Amazing Attack
- Excellent Offensive typing
- Slow and Bulky
- Gets Bulk Up
- Booster Energy Protosynthesis attack boost can't be removed
Koraidon/Miraidon:
- Both hit very hard
- Koraidon gets Swords Dance while Miraidon gets Calm Mind
- Their abilities are very good
You can find movesets for them on their respective moveset threads.
Edit:
Azumarill:
- Hits very hard (Thanks to Huge Power)
- Water/Fairy is a good combo
- Belly Drum
- Slow and has a good hp stat
(Thank you Amethyst!)
Kingambit:
- Slow and Bulky
- Massive attack
- Swords Dance
- Alright offensive type