Can Grimlock give himself Bold 3 with his ability.

Yes. Grimlock Dinobot. Grimlock count.

How does Grimlock’s ability work?

Let’s say Grimlock attacks a character with 10 health and 8 damage counters. If he does 4 attack damage to that character, 2 of that damage is enough to KO the defender. For the extra 2 damage, your opponent chooses one of their other characters. That character would get 2 damage counters.

Let’s say the extra damage is enough to KO a second character. Does the extra damage keep going to a third character?

No. The extra damage isn’t attack damage. Continuing the previous example, your opponent could choose a character with 12 health and 11 damage counters and do 2 more damage to it. That character would be KO’d.

With Showing Off, would a Bot receive any and all "when you flip to" triggers during the process or does it only count the final mode it's flipped to? For example, if Grimlock - Dinobot Leader is in bot mode and plays Showing Off, could he end in Bot mode with the Bold 3 from his Alt mode?

Yes, you can first flip Grimlock to alt mode, causing the ability on that mode to trigger, and then flip back to bot mode.

When I play Steamroll on Grimlock, does the "spillover" damage occur twice?

No. Both abilities are practically identical, so one of them will apply (you can choose), but then the other one will not apply.

A situation came up today after Grimlock in bot mode (Wave 1) attacked Motor Master in truck mode. Does the extra damage carry over if Motor Master is KO’d? We couldn’t quite figure out the timing. If Motor Master is KO’d, does his ability then not work, or is the extra damage assigned prior to the KO?

In this scenario, Motormaster would be KO’d and his ability would not apply. Grimlock’s ability will trigger after Motormaster is KO’d.

Does Grimlock's bot mode’s extra damage count as attack damage? If it does, and assuming Grimlock has 5 or more extra damage, how much damage does it do in the following situations: A. Damage is assigned to a bit with Force Field equipped. B. Damage is assigned to Insecticon Skrapnel in bot mode. C. Any bot that is protected by Motormaster alt mode skill.

The extra damage is not attack damage, so if you are redirecting to a bot-mode Skrapnel or a character with a force field on it, they will take the full additional damage. On the other hand, a damage-capping effect on the character you’re attacking will be relevant. So, if you have a Skrapnel in bot-mode with 5 damage on him and Grimlock attacks him for say 10 damage, that damage will be reduced to 3 by Skrapnel’s ability, 2 of it will KO him, and the last point will be assigned to another character of the defending player’s choice.

Grimlock in Bot mode attacks with 10 attack. Insecticon Skrapnel in Bot mode defends with 0 defense and 1 hp remaining. What would the transferred damage be? Will it transfer 2 damage or 9 damage?

Two damage!

So the board is 1 Grimlock on Player 1’s side and a Metroplex and Scamper on Player 2’s side. Player 1 attacks Metroplex since Scamper is untapped and unable to be targeted. Then Grimlock gets enough attack to kill both characters with skill since Metroplex is heavily damaged and Scamper has low defense and life. So, since the Grimlock attacked Metroplex while Scamper had Heroism, I assume that since Heroism only changes where the damage goes and not the actual attack that the damage a character takes through the effect of Heroism is effect damage and not battle damage. I want to know the ruling because if the damage IS battle damage then Grimlock’s skill does trigger and Player 2 loses, since Scamper would die as the rollover would kill Metroplex but if it is effect damage, then Grimlock’s skill wouldn't trigger and only Scamper would be KO’d.

The damage redirected by Heroism is still attack damage. So Scamper would take enough to get KO’d and then Grimlock’s ability would trigger and the defender would have to assign the extra damage to Metroplex.

What happens when you put the Steamroll action on Grimlock - Dinobot Leader and he KO's a character with excessive damage? Does it only do the effect of one or the other, or does it stack?

Only one effect will work. There’s no extra damage after the first effect applies.