Voting for counter and for check.
I like Shedinja as a counter; only works on stall but I do think Shed takes stall to new dimensions in Natdex OU, even with Safety Goggles since Mega Sableye exists to support it. Mega Latias is really solid, sometimes I find it gets chipped into KO range coming in a turn after Manaphy, like from Roosting off Mega Swampert Ice Punch, Stealth Rock chip when Greninja doubles in on you, etc.
For checks I like Rilla, always gives Manaphy second thoughts about a Tail Glow and doesn't get as chipped as Koko from a Surf on the switch due to terrain recovery.
I like Shedinja as a counter; only works on stall but I do think Shed takes stall to new dimensions in Natdex OU, even with Safety Goggles since Mega Sableye exists to support it. Mega Latias is really solid, sometimes I find it gets chipped into KO range coming in a turn after Manaphy, like from Roosting off Mega Swampert Ice Punch, Stealth Rock chip when Greninja doubles in on you, etc.
For checks I like Rilla, always gives Manaphy second thoughts about a Tail Glow and doesn't get as chipped as Koko from a Surf on the switch due to terrain recovery.