Psionic Entity: Onslaught can't be the target of other characters's Incapacitate, Mind Control, Penetrating/Psychic Blast, or Perplex.

Reality Warp: Once during your turn, as a free action choose two single-base characters within range and line of fire and place them in each other's squares.

Heroic Sacrifice: When turning the dial, stop turning the dial when this click is revealed. When this click is revealed, an opponent may KO character(s) they control of 100 or more total points. If they do, one of those characters deals Onslaught 1 unavoidable damage. If they don't, Onslaught can use Impervious. This power can't be countered.

Xavier's Dark Side: Onslaught can use Outwit. When he uses it to counter a standard power, you may counter all other powers with the same color as the chosen power on all opposing characters within 10 squares and line of fire.

See the Colossal Stamina and Great Size entries for more information.

If I have a character with more than one , can I uses Penetrating/Psychic Blast to target Onslaught and another character and then just not deal penetrating damage to Onslaught?
No. If you want to use P/PB, you can't target Onslaught.

I don't really understand what Heroic Sacrifice does...
First, if Onslaught's last click appears, stop turning the dial no matter how much damage was actually dealt to him.

Now, when this power appears, the opposing player has a choice: he can either KO at least 100 points of his own characters to deal 1 unavoidable damage to Onslaught, which would also KO Onslaught; or he can keep his team intact (or if he doesn't have 100 points to KO) and let Onsalught stay in the game on his last click and using Impervious.

What happens if we're playing with more than 2 players? Who do I get to choose to KO 100 points first or does one of the other players go first?
The active player would get first dibs (probably the player that damaged Onslaught on to that click in the first place). If that player declines to KO 100 points of characters, go around the map in play order; for example, if player 1 is Onslaught's controller and player 2 is the currently active player, but player 2 declines, now player 3 can decide if he wants to KO his characters.

When Onslaught counters a standard power, and all ther powers with the same color, does that only counter powers currently showing on the dials?
No. Let's say Onslaught counters Professor X's Outwit; that would also counter Wolverine's Stealth (if Onsluaght could have draw line of fire to Wolverine in the first place, see the power description above) and all other standard powers with a black square. Onslaught then attacks Wolverine and after taking damage Regeneration appears on Wolverine's dial. Since all black powers are still countered (the effects of Outwit don't end until the beginning of Onslaught's next turn), Wolverine's Regeneration is also countered.

Clarified an example.